Technical Reference

Plastic Resin Shrinkage Rate Chart for Injection Molding

Plastic resin shrinkage rate chart for ABS PC Nylon PP PE POM PMMA PBT and glass-filled materials

Compare typical plastic resin shrinkage values for ABS, PC, Nylon, PP, PE, POM, PMMA, PBT, PBT GF30, PA66 GF30 and other glass-filled materials. Use this injection molding shrinkage chart as an early reference for mold steel allowance, dimensional risk, warpage tendency, cavity layout and DFM review before tooling. Shrinkage values should not be used as final steel dimensions alone; final cavity compensation should be confirmed with the selected resin datasheet, wall thickness review, gate location, processing window, Moldflow analysis, T0/T1 tool trial results and dimensional inspection.

Quick Engineering Answer

Plastic resin shrinkage rate is the percentage a molded part contracts after cooling. ABS, PC and PMMA usually have lower shrinkage, while PP, PE, POM and Nylon often shrink more. Glass-filled grades such as PBT GF30 and PA66 GF30 may shrink differently in flow and transverse directions. Final shrinkage depends on resin grade, filler content, wall thickness, gate location, packing pressure, mold temperature, cooling balance, Moldflow review and tool trial results.

For a practical shrinkage or warpage risk review, send your 2D drawing, 3D CAD, target resin grade, tolerance requirements, surface finish criteria, assembly fit requirements and expected production volume. Our engineering team can review material shrinkage behavior, wall thickness, gate location, flow direction, cooling balance and inspection requirements through a focused DFM review and Moldflow analysis before final mold steel dimensions are released.

Send Drawing for Shrinkage & DFM Review Compare Resin Selection Criteria

Plastic Resin Shrinkage Rate Chart

Use this plastic resin shrinkage rate chart to compare common injection molding materials by typical shrinkage value, resin type, dimensional risk and DFM concern. It covers ABS, PC, PC/ABS, Nylon, PP, PE, POM, PMMA, PBT, PA66-GF30, PBT-GF30 and high-temperature plastics used for housings, connectors, gears, clips, covers and functional molded parts. Use these values as early mold design references only. Final shrinkage allowance should be confirmed with the selected resin supplier datasheet, filler content, wall thickness, gate location, flow direction, processing window, inspection method and T0/T1 tool trial results.

Plastic Shrinkage Rate Table for Common Injection Molding Resins

Plastic Resin Common Name Typical Shrinkage Rate (%) Shrinkage Risk Resin Type DFM / Mold Design Note
ABS Acrylonitrile Butadiene Styrene 0.40 – 0.70 Low Amorphous ABS shrinkage value is usually stable for housings, covers and snap-fit features. Review thick bosses, ribs and local wall transitions for sink marks, cosmetic distortion and fit drift.
PC Polycarbonate 0.50 – 0.70 Medium Amorphous PC shrinkage is relatively low, but gate stress, optical stress, molded-in stress and notch sensitivity can affect transparent or impact-loaded parts. Review gate location and inspection criteria before steel cut.
PC/ABS PC ABS Blend 0.40 – 0.70 Low Amorphous blend PC/ABS shrinkage is suitable for enclosure fit and cosmetic surfaces. Check boss bases, ribs, screw towers and clip features where uneven packing can create sink or assembly mismatch.
PMMA Acrylic 0.30 – 0.70 Low Amorphous PMMA has low shrinkage but high cosmetic and cracking sensitivity. Review gate stress, polished surface requirements, flow marks and edge cracking risk for optical or transparent parts.
PS Polystyrene 0.40 – 0.70 Low Amorphous PS shrinkage is low, but the material is brittle. Avoid using shrinkage stability as the only design criterion; check impact load, snap-fit stress and continuous flexural load constraints.
PP Polypropylene 1.50 – 2.20 High Semi-crystalline PP shrinkage rate is high and strongly affected by wall thickness, packing pressure, gate size and cooling balance. Flat parts, lids and living-hinge features should be checked for warpage before tooling.
HDPE High-Density Polyethylene 1.50 – 3.00 High Semi-crystalline HDPE shrink rate is high and can create cavity allowance, roundness and flatness risk. Review wall thickness, cooling layout, ejection support and tolerance expectations before tool steel sizing.
LDPE Low-Density Polyethylene 1.50 – 3.50 High Semi-crystalline LDPE has high shrinkage and flexible part deformation risk. Keep wall thickness uniform, confirm ejection direction and avoid applying tight dimensional tolerances without trial-based validation.
POM Acetal 1.80 – 2.50 High Semi-crystalline POM shrinkage value is high and important for gears, bushings, sliding parts and precision mechanical features. Check gear pitch, roundness, datum features, bore size and CMM or functional gage inspection plan.
PA6 Nylon 6 0.70 – 2.20 High Semi-crystalline Nylon shrinkage varies by grade, moisture condition and filler content. Review drying, post-mold conditioning, assembly fit and dimensional inspection timing before locking mold steel dimensions.
PA66 Nylon 66 1.00 – 2.00 High Semi-crystalline PA66 shrinkage is sensitive to crystallinity, moisture absorption and processing conditions. Critical fits should be validated with material certificate review, controlled molding conditions and FAI inspection.
PA66-GF30 Glass-Filled Nylon 0.30 – 0.80 Medium Filled semi-crystalline PA66 GF30 shrinkage is lower in total value but can become directional due to fiber orientation. For connector housings, brackets and structural parts, verify flow direction, gate location and warpage risk through Moldflow analysis.
PBT Polybutylene Terephthalate 1.20 – 2.00 Medium Semi-crystalline PBT shrinkage matters for connector bodies, terminal spacing and small functional features. Check pitch tolerance, pin clearance, mold temperature, packing stability and fixture-based inspection requirements.
PBT-GF30 Glass-Filled PBT 0.30 – 0.90 Medium Filled semi-crystalline PBT GF30 shrinkage is often directional and should not be treated as one uniform number. Review fiber orientation, gate position, cavity balance, terminal pitch and CMM or fixture inspection before tooling release.
PET Polyethylene Terephthalate 1.20 – 2.00 Medium Semi-crystalline PET shrinkage depends on drying, crystallization and mold temperature control. Confirm drying conditions, tool temperature stability and dimensional release criteria for production parts.
TPU Thermoplastic Polyurethane 0.80 – 2.00 Medium Elastomer TPU shrinkage varies with hardness, flow length and wall thickness. Check overmolding bond area, substrate geometry, ejection deformation and final fit after relaxation.
TPE Thermoplastic Elastomer 1.00 – 2.50 High Elastomer TPE shrinkage can create fit drift and ejection deformation in soft-touch or overmolded parts. Review substrate compatibility, mechanical lock design, flow length and inspection method.
PPS Polyphenylene Sulfide 0.60 – 1.50 Medium High-temp semi-crystalline PPS shrinkage depends on filler content, wall thickness and processing stability. Filled PPS parts should be checked for fiber orientation, warpage, concentricity and CTQ inspection strategy.
PEI Polyetherimide 0.50 – 0.80 Medium High-temp amorphous PEI has good dimensional stability, but high mold temperature and processing control are still required. Review heat resistance, gate stress, tolerance feasibility and inspection criteria.
PEEK Polyetheretherketone 1.00 – 1.50 Medium High-temp semi-crystalline PEEK shrinkage requires high-temperature tooling, controlled mold temperature and stable process windows. Confirm material grade, crystallinity, critical tolerances and validation method before production tooling.

Engineering Notice: Resin shrinkage values in this chart are early mold design references, not final cavity steel dimensions. Always verify shrinkage assumptions against the selected resin datasheet, filler content, ASTM D955-style test data, wall thickness, gate location, flow direction, cooling balance, processing window and T0/T1 tool trial results. For active tooling projects, confirm shrinkage, warpage and tolerance risk with a structured DFM review before finalizing mold layout and cavity compensation.

What Is Shrinkage Rate in Injection Molding?

Shrinkage-Affected CTQ Features

Plastic shrinkage can change critical-to-quality dimensions after cooling. Review shrinkage risk on these features before mold steel dimensions are released:

  • Wall thickness transitions, ribs and boss areas with sink or local distortion risk
  • Snap-fit hooks, sealing surfaces and mating-part clearance zones
  • Flatness areas, long flow paths, thin walls and large panel surfaces
  • Pin alignment, connector pitch, gear pitch, bore roundness and datum-related features

Shrinkage rate in injection molding is the dimensional reduction between the mold cavity size and the final cooled plastic part. It is usually expressed as a percentage of the original cavity dimension. For example, if a resin has higher shrinkage, the cavity may need additional steel allowance so the molded part reaches the required final size after cooling. This value affects mold steel compensation, tolerance feasibility, flatness, snap-fit clearance, sealing surfaces, connector alignment and final assembly fit.

A plastic resin shrinkage value should be reviewed during DFM, mold design, tool trial and inspection planning. The chart value is only an early reference; the final result must be checked against the selected resin supplier datasheet, filler content, ASTM D955-style test data, wall thickness, gate location, processing window, cooling balance and T0/T1 tool trial results.

Why Plastic Shrinkage Matters for Mold Design

Plastic shrinkage must be reviewed before mold steel is cut because cavity dimensions are normally offset to compensate for expected resin contraction. If the shrinkage rate is underestimated, the molded part may become undersized, out of tolerance or difficult to assemble. If it is overestimated, the tool may require steel correction, dimensional adjustment or additional T0/T1 trial work. Review wall thickness, ribs, bosses, gate location, cooling layout and tolerance targets early with Injection Molding Design Guidelines & DFM Standards.

Why Shrinkage Rate Is Not a Fixed Number

A resin shrinkage chart is an early reference only because final shrinkage changes with material grade, filler content, wall thickness, gate location, packing pressure, mold temperature, cooling time, flow direction and cavity balance. For high-shrinkage, glass-filled, thin-wall, large flat or multi-cavity parts, use Moldflow analysis before tooling to review fill balance, packing behavior, cooling imbalance, fiber orientation and warpage risk.

Why Some Plastic Resins Shrink More Than Others

Plastic resin shrinkage comparison for amorphous semi-crystalline and glass-filled injection molding materials

Plastic resins shrink at different rates because their polymer structure, crystallinity, filler content, moisture behavior and cooling response are different. This is why ABS, PC and PMMA shrinkage values are usually lower and more stable, while PP, PE, POM, Nylon and PBT shrinkage rates are often higher and more sensitive to processing conditions. For mold design, the shrinkage number should be treated as a starting assumption, not a fixed steel compensation value.

Separating amorphous, semi-crystalline and glass-filled resins helps tooling teams review mold steel allowance, runner balance, gate location, cooling layout, fiber orientation and inspection strategy before mold steel is finalized. For material decisions, compare shrinkage data with the Injection Molding Material Selection Guide before selecting the final resin. Final shrinkage still depends on grade-specific datasheets, filler percentage, packing pressure, mold temperature, cooling balance, flow direction and T0/T1 tool trial results.

Amorphous Plastics: ABS, PC, PMMA and PS

Amorphous plastics such as ABS, PC, PMMA and PS usually have lower and more predictable shrinkage than semi-crystalline plastics. ABS shrinkage values are often used for housings, cosmetic covers and snap-fit features, while PC and PMMA require extra attention to gate stress, molded-in stress and optical appearance. These materials can still show dimensional drift when wall thickness, packing pressure or cooling balance is not controlled.

In a plastic shrinkage rate table, ABS and PC usually show lower shrinkage than PP, PE, POM and Nylon, but low shrinkage does not automatically mean low tooling risk. For ABS and PC/ABS enclosures, check boss bases, ribs, screw towers and clip areas for sink marks and assembly mismatch. For clear PC or PMMA parts, review shrinkage, gate stress, residual stress and polishing requirements before finalizing cavity steel; optical inspection or polariscope review may be needed when stress visibility is critical.

Semi-Crystalline Plastics: PP, PE, POM, Nylon and PBT

Semi-crystalline plastics such as PP, PE, POM, Nylon and PBT usually shrink more because crystallization creates additional volume change during cooling. PP and PE shrinkage rates are important for flat panels, lids, snap features and sealing surfaces. POM shrinkage values matter for gears, bushings, sliding parts and roundness control. Nylon shrinkage can change with moisture conditioning, while PBT shrinkage affects connector pitch, terminal clearance and small functional features.

These resins need closer DFM review for wall thickness, ribs, bosses, gate location, flow length, cooling balance, cavity steel allowance and CTQ dimensions before offsets are locked. Use Injection Molding Design Guidelines to review geometry conditions when semi-crystalline resins are used. For PP, PE, POM, Nylon and PBT parts with flatness, roundness or assembly risk, validate the assumptions with Moldflow review, flatness inspection, functional gages or FAI after tool trials.

Glass-Filled Resins: PA66-GF30, PBT-GF30 and PPS-GF

Glass-filled resins such as PA66-GF30, PBT-GF30 and PPS-GF usually show lower total shrinkage than unfilled grades, but they can create directional shrinkage because fibers align with the flow direction. This is why PA66 GF30 shrinkage and PBT GF30 shrinkage should not be treated as one uniform value. Flow-direction shrinkage, transverse shrinkage and fiber orientation can affect connector housings, pin alignment, flatness, clips, brackets and structural parts differently.

For glass-filled nylon, PBT-GF30 or PPS-GF parts, use Moldflow analysis to review gate location, fiber orientation, fill balance and warpage risk before finalizing the tool layout. After T0/T1 trials, validate pin alignment, datum features, flatness and critical dimensions with fixture inspection, CMM inspection or FAI before releasing the mold for production.

ABS, PC, Nylon, PP, PE and POM Shrinkage Comparison

The most common plastic shrinkage questions compare ABS, PC, Nylon, PP, PE and POM because these materials are widely used for molded housings, gears, connectors, covers, clips, bushings and mechanical parts. ABS and PC usually have lower shrinkage values and better dimensional stability, while PP, PE, POM and Nylon often need closer DFM review because higher shrinkage can affect flatness, roundness, pitch accuracy, sealing surfaces and assembly fit.

ABS vs PC vs Nylon vs PP vs PE vs POM Shrinkage Comparison

Material Shrinkage Behavior Better For Watch Out For
ABS Low shrinkage value, typically 0.40 – 0.70% Housings, covers, cosmetic parts, snap-fit features and enclosure components Sink marks around thick bosses, ribs, screw towers, local wall transitions and cosmetic surfaces
PC Low to medium shrinkage value, typically 0.50 – 0.70% Clear parts, impact-resistant parts, lenses, covers and structural housings Gate stress, birefringence, optical distortion, residual stress and cracking near sharp corners
Nylon Medium to high shrinkage, grade-dependent, typically 0.70 – 2.20% Structural parts, wear-resistant parts, clips, brackets, gears and functional molded components Moisture absorption, post-mold dimensional drift, conditioning effect, assembly fit and tolerance stability
PP High shrinkage rate, typically 1.50 – 2.20% Living hinges, lightweight parts, chemical-resistant parts, caps, lids and flexible features Warpage, flatness loss, shrinkage mismatch, long flow paths, cooling imbalance and large panel deformation
PE High shrinkage rate, typically 1.50 – 3.50% Chemical-resistant parts, flexible parts, containers, caps and low-friction molded components Large cavity allowance, cooling variation, roundness drift, flatness risk and ejection deformation
POM High shrinkage value, typically 1.80 – 2.50% Gears, bushings, sliding parts, precision mechanisms, cams and low-friction functional parts Roundness, gear pitch accuracy, bore size, datum features, shrink drift and CMM or functional gage validation

Which Plastic Has the Lowest Shrinkage?

ABS, PC, PMMA and PS usually have the lowest plastic shrinkage values among common injection molding materials. These amorphous plastics are often preferred when part fit, cosmetic surface, enclosure alignment and dimensional consistency are important.

Low shrinkage does not remove DFM risk. Final ABS shrinkage value or PC shrinkage value still depends on resin grade, wall thickness, boss design, gate location, packing pressure and cooling balance. For mating clearances, snap-fits, screw towers, sealing surfaces or optical features, review CTQ dimensions with DFM review before cavity steel dimensions are finalized. For PC or PMMA clear parts, use visual optical inspection or polariscope review when gate stress or residual stress is critical.

Which Plastic Has the Highest Shrinkage?

PE, PP, POM and some Nylon grades usually have the highest plastic shrinkage rates. These semi-crystalline plastics can be suitable for chemical resistance, living hinges, sliding parts, wear resistance or mechanical function, but they require closer review of wall thickness, gate location, flow length, cooling balance and inspection method.

For high-shrinkage semi-crystalline resins, compare the material choice with the Injection Molding Material Selection Guide, then use Moldflow analysis, flatness fixtures, CMM inspection or FAI when dimensional risk is high. For PP, PE, POM and Nylon parts with flatness, roundness, gear pitch or assembly fit risk, dimensional validation after T0/T1 tool trials is essential.

How Shrinkage Rate Affects Mold Steel Dimensions

Injection mold cavities are normally designed larger than the final plastic part because the resin contracts during cooling. This cavity compensation is often called mold shrinkage allowance or mold steel allowance. The correct allowance depends on resin shrinkage value, wall thickness, ribs, bosses, gate location, packing pressure, cooling balance, flow direction, CTQ dimensions and inspection method. Shrinkage charts help estimate the first steel condition, but final cavity dimensions should be confirmed through DFM review, Moldflow analysis, T0/T1 tool trials, FAI, CMM or fixture inspection.

Injection Mold Shrinkage Allowance

Injection mold shrinkage allowance is the cavity size compensation used to offset expected plastic contraction after cooling. For lower-shrinkage resins such as ABS, PC, PC/ABS or PMMA, the allowance is usually smaller and more predictable, but local sink, boss distortion and cosmetic fit still need review.

For high-shrinkage resins such as PP, PE, POM, Nylon and some PBT grades, review cavity offsets, wall thickness, ribs, bosses, gate location, flow length and cooling layout with Injection Molding Design Guidelines before steel cut. Shrinkage allowance should be treated as an initial mold sizing reference and confirmed with resin datasheet values, CTQ dimension review, processing window control and T0/T1 tool trial results.

Why One Shrinkage Value Cannot Define the Whole Mold

One shrinkage value cannot define the whole mold because different part features cool, pack and deform differently. Thick bosses, ribs, long flow paths, flat sealing surfaces, thin-wall sections, gear teeth, pin holes and connector pitch areas may not shrink at the same rate or in the same direction.

CTQ dimensions should be reviewed separately during DFM review and tool layout planning before cavity steel dimensions are released. Review snap-fit clearance, sealing surfaces, pin alignment, gear pitch, bore roundness, flatness and datum features separately instead of applying one average shrinkage value across the entire mold.

Mold Steel Compensation for High-Shrinkage Resins

High-shrinkage resins may require steel-safe strategies around critical dimensions. Engineers should review flow direction, wall transitions, gate location, cooling channel layout, packing pressure, cavity balance and tolerance risk before finalizing mold steel compensation.

For glass-filled or semi-crystalline materials, use Moldflow analysis to review fill balance, packing behavior, fiber orientation, cooling imbalance and warpage risk before confirming tool offsets. Confirm steel-safe decisions with Moldflow results, T0/T1 samples, FAI, CMM data, flatness fixtures or dedicated functional gages.

Engineering Note

Mold steel dimensions should use resin shrinkage data as an early reference only. Before production approval, review flow direction, wall transitions, ribs, bosses, gate location, cooling layout, cavity balance and CTQ dimensions. For high-shrinkage, glass-filled or tight-tolerance parts, verify cavity offsets with Moldflow validation, T0/T1 trial samples, FAI, CMM inspection, flatness fixtures, cavity-to-cavity comparison or functional gauges before releasing the mold for production.

Shrinkage Risk by Part Geometry

Plastic shrinkage risk is not only a material issue. The same resin can shrink differently depending on wall thickness, flow length, ribs, bosses, gates, flat surfaces, sealing grooves, gear teeth, connector pitch and assembly features. A shrinkage rate chart should be used together with geometry review, DFM review, Moldflow analysis, tool trial feedback and inspection planning before cavity steel dimensions are finalized.

Injection Molding Shrinkage Risk Matrix

Part Geometry Shrinkage Risk Typical Result Recommended Review
Thick boss or screw post Local sink, voids and uneven shrinkage around thick sections Weak screw post, cosmetic sink mark, delayed assembly failure or local dimension drift Wall thickness and boss design review
Long flat cover or panel Bowing, twist and warpage caused by uneven cooling or packing Assembly mismatch, visible gap, sealing failure or flatness out of tolerance Moldflow analysis + flatness fixture check
Snap-fit housing Clearance drift and local shrinkage around hooks, slots and mating features Loose fit, tight fit, clip fracture or inconsistent assembly force FAI + CMM check + functional fit test
Connector housing Pin alignment error, terminal pitch drift and cavity-to-cavity variation Terminal mismatch, insertion force issue, electrical contact risk or assembly rejection Terminal gauge, datum fixture, cavity-to-cavity comparison or CMM datum check
Gear, bushing or round feature Pitch error, roundness error, bore shrinkage and non-uniform radial contraction Noise, wear, poor rotation, press-fit failure or functional mechanism drift CMM profile check, gear gauge, bore gauge, pitch inspection or functional rotation test
Clear lens or optical cover Optical stress, birefringence, molded-in stress and gate-area distortion Visible distortion, cracking risk, poor transparency or optical performance loss Polariscope review, visual optical inspection, gate-area check and residual stress review
Multi-cavity part Cavity-to-cavity shrinkage variation caused by imbalance in filling, packing or cooling Inconsistent fit, cavity-specific dimensional drift or unstable production release Cavity balance review, cavity-to-cavity FAI and process window check

High-Risk Features for Plastic Shrinkage

Features that increase shrinkage-related risk include thick wall sections, abrupt wall transitions, tall ribs, deep bosses, long flow paths, large flat surfaces, sealing grooves, snap-fits, gears, bushings, connector pitch features, multi-cavity layouts and transparent optical surfaces. Before mold steel dimensions are released, review these features for wall uniformity, gate location, cooling balance, packing access, ejection risk, datum strategy and inspection method with a targeted DFM review.

When Shrinkage Needs DFM or Moldflow Review

Shrinkage should be reviewed with DFM or Moldflow when the resin, geometry or tolerance requirement creates dimensional risk before mold steel is cut. A shrinkage chart can identify early risk points, but high-risk parts need DFM review, Moldflow analysis and inspection planning before final cavity compensation is released.

DFM and Moldflow Trigger Table

Condition Why It Matters Recommended Action
Shrinkage > 1.2% Higher risk of dimensional drift across wall transitions, flatness areas and CTQ features DFM review + Moldflow analysis
Glass-filled resin Fiber orientation can create directional shrinkage, twist, connector pitch drift and warpage Moldflow fiber-orientation review before gate location and tool layout are finalized
Tight tolerance Small dimensional errors can affect assembly fit, sealing surfaces, datum features or functional clearance FAI, CMM and fixture inspection plan for CTQ dimensions, datum features and functional clearance
Large flat surface Uneven cooling can increase warpage, bowing, twist and flatness variation Review gate location, cooling balance and packing access, then verify flatness with a fixture or CMM after T0/T1 tool trials
Multi-cavity mold Fill balance, packing pressure and cooling variation can create cavity-to-cavity dimensional differences Use runner balance review, cavity-to-cavity FAI, cavity ID tracking and process window check to control dimensional variation
Clear or optical part Gate stress, residual stress and shrinkage mismatch can create birefringence, haze or optical distortion Use gate location review, packing pressure control, polariscope review and visual optical inspection
Connector housing Terminal pin alignment, pitch drift and datum mismatch can compromise mating clearance Use terminal gauge, datum fixture, cavity-to-cavity comparison and CMM datum check
Gear, bushing or round part Pitch accuracy, bore shrinkage and out-of-roundness errors can drive noise, wear or poor rotation CMM profile check, bore gauge, concentricity check, gear gauge inspection or functional rotation test

Quick Answer: When Is Moldflow Needed for Shrinkage?

Quick Engineering Answer

Moldflow is recommended when a part uses high-shrinkage resin, glass-filled material, tight tolerance, thin walls, long flow length, large flat surfaces, connectors, gears, optical features or multi-cavity tooling. It helps review fill balance, packing behavior, fiber orientation, sink risk and warpage before cavity steel dimensions are finalized. Confirm high-risk parts with FAI, CMM, fixture or optical inspection after tool trials.

Common Mistakes When Using a Shrinkage Rate Chart

A shrinkage rate chart is useful for early mold design, but it can cause dimensional errors when teams treat chart values as final cavity compensation. Common mistakes include ignoring part geometry, resin grade, filler content, fiber orientation, gate location, cooling balance, process window and validation methods such as Moldflow, FAI, CMM or fixture checks. Use shrinkage values as engineering assumptions that must be confirmed before production release.

Treating Datasheet Shrinkage as Final Part Shrinkage

Resin datasheet shrinkage values are usually measured from standard test plaques under controlled molding conditions, not from the final production geometry. A real molded part can shrink differently because of wall thickness transitions, gate location, flow direction, packing pressure, mold temperature, cooling balance and cavity-to-cavity variation.

Engineering Validation: Confirm datasheet shrinkage with the selected resin grade, supplier datasheet, ASTM D955-style test data, part geometry review, approved processing window and T0/T1 tool trial samples before steel dimensions are released for production.

Using One Shrinkage Value for the Entire Mold

Shrinkage patterns vary across different features of the same part. Thick bosses, thin walls, ribs, flat sealing surfaces, long-flow sections, gear teeth and connector pitch areas can shrink at different rates or in different directions. CTQ dimensions should be reviewed individually instead of applying one average shrinkage value across the entire cavity.

Engineering Validation: Verify CTQ dimensions with FAI, CMM inspection, fixture checks, functional gages and cavity-to-cavity comparison after T0/T1 tool trials before launching high-volume production.

Ignoring Filler Content and Fiber Orientation

Glass fibers, mineral fillers and flame-retardant additives can change a resin’s base shrinkage behavior. Glass-filled grades such as PA66-GF30, PBT-GF30 and PPS-GF may reduce total shrinkage, but fiber orientation can increase directional shrinkage, twist, connector pitch drift and warpage. Use Moldflow analysis before tooling when pin alignment, flatness, datum control or assembly fit is critical.

Engineering Validation: Review fiber orientation, gate location, flow direction, weld line position, warpage risk and pin alignment before tool layout is finalized, then confirm with CMM, fixture inspection or FAI after tool trials.

Ignoring Mold Temperature and Packing Pressure

Melt temperature, mold temperature, packing pressure, cooling time and transfer position can change final molded dimensions. If the process window changes between tool trials and production, shrinkage-related dimensions may drift from the drawing tolerance even when the mold steel was initially correct.

Engineering Validation: Use trial data, approved molding conditions, process window records and dimensional inspection results to confirm whether shrinkage remains stable from T0/T1 trials to continuous production.

Changing Resin After Steel Cut Without Engineering Review

Changing a resin grade after steel cut can change shrinkage value, flow length, packing behavior, cooling response, ejection force, surface finish and final molded dimensions. Even a similar material family can behave differently when filler percentage, impact modifier, flame retardant package or supplier grade changes. Material substitutions should be checked with an engineering DFM review, updated shrinkage assumptions and dimensional inspection planning before production approval.

Engineering Validation: After a resin change, recheck shrinkage assumption, flow length, gate location, cooling balance, ejection risk, CTQ dimensions and inspection plan. For tight-tolerance or high-volume parts, confirm the change with T0/T1 samples, FAI, CMM or fixture inspection before production approval is locked.

Inspection Methods for Shrinkage-Related Dimensional Risk

Shrinkage-related dimensional risk should be verified with the right inspection method after T0/T1 tool trials. The correct method depends on whether the part shows clearance drift, flatness change, pin alignment error, roundness deviation, optical stress, CTQ dimension risk or cavity-to-cavity variation. For production approval, shrinkage validation should connect the drawing datum scheme, molded sample data, cavity number, process window and inspection report.

Inspection Methods for Injection Molding Shrinkage Risk

Shrinkage-Related Risk Inspection Method Use Case
Snap-fit clearance drift FAI / CMM / functional fit test ABS, PC/ABS and PC housings with clips, screw towers, hooks or mating clearance requirements
Flatness change Flatness fixture / CMM with datum reference / surface plate check PP, PE, POM, Nylon or large flat parts where warpage affects sealing, assembly or cosmetic fit
Pin alignment error Terminal gauge, datum fixture, cavity comparison or CMM datum check PA66-GF30, PBT-GF30 and glass-filled connector housings with terminal pitch or mating alignment risk
Roundness / pitch error CMM profile / gear gauge / bore gauge / pitch inspection POM gears, bushings, cams, rotating features and low-friction mechanical parts
Optical stress Polariscope review, visual optical inspection, gate-area check and residual stress review PC, PMMA and transparent covers where birefringence, haze, cracking or optical distortion is critical
Cavity variation Cavity balance review, cavity-to-cavity FAI, cavity ID tracking and process window check Multi-cavity molds where filling, packing, cooling or shrinkage variation creates inconsistent fit
Sealing surface mismatch CMM / leak fixture check / datum-based flatness inspection Covers, housings, fluid parts and sealing interfaces where shrinkage can create leakage or assembly gaps

Why FAI and CMM Matter for Shrinkage Validation

First Article Inspection (FAI) and Coordinate Measuring Machine (CMM) inspection verify whether molded dimensions match the expected shrinkage allowance after T0/T1 tool trials. For critical-to-quality (CTQ) features, compare molded part data against the 2D drawing, datum scheme, cavity number, inspection method and approved Scientific Molding process window. These inspection records help confirm repeatable production, cavity-to-cavity consistency and process stability before production approval.

Example: PP vs ABS Shrinkage Risk Before Tooling

PP vs ABS shrinkage comparison for flatness mating fit mold steel allowance and DFM review

Note: This example compares PP and ABS for a molded housing or cover before tooling. PP and ABS are often compared when engineering teams need to balance chemical resistance, living hinge function, cost, cosmetic surface, mating fit and dimensional stability. Because PP usually has a higher shrinkage rate than ABS, the two materials may require different mold steel allowance, gate location, cooling layout, packing strategy and inspection plans.

ABS is amorphous and usually has lower, more predictable shrinkage. PP is semi-crystalline and usually has higher shrinkage with greater flatness and warpage risk. Before final material approval, confirm the selected grade with resin datasheets, DFM review, tool trial inspection and the Injection Molding Material Selection Guide.

PP Housing with Flatness Risk

A large molded cover made from PP may have higher shrinkage and flatness risk than the same geometry made from ABS. PP can be useful for chemical resistance, low density or living hinge performance, but its higher shrinkage rate requires closer review of wall thickness, ribs, gate location, flow length, packing pressure and cooling balance.

Abrupt wall transitions, uneven ribs and large flat surfaces can increase PP warpage risk before the first tool trial. For wide PP covers, use Moldflow analysis when long flow length, uneven cooling, sealing surfaces or tight assembly fit are present. After T0/T1 trials, verify flatness, sealing areas and assembly fit with a flatness fixture, CMM inspection or functional fit check.

ABS Housing with Dimensional Fit Requirement

ABS usually offers lower and more predictable shrinkage for housings, covers and snap-fit parts. It may be a better option when mating fit, cosmetic surface, enclosure alignment and dimensional consistency are more important than chemical resistance or living hinge function. DFM should still review thick bosses, ribs, screw towers and sink risk.

Because ABS is amorphous, cavity offsets are usually more stable than PP, but final dimensions still depend on wall thickness, gate location, packing pressure, cooling balance and T0/T1 trial results. For ABS housings, verify snap-fit clearance, boss sink, sealing surfaces, mating features and cosmetic fit with FAI, CMM or fixture inspection after tool trials.

Recommended Validation Method

For PP, use Moldflow and flatness inspection when large surfaces, uneven ribs, long flow paths or sealing areas are present. For ABS, use FAI, CMM or fixture checks on snap-fit clearance, boss areas, sealing surfaces and mating features. In both cases, final shrinkage should be confirmed with tool trial samples rather than chart values alone.

For multi-cavity or large flat parts, use Moldflow analysis before steel cut to review fill balance, packing behavior, cooling imbalance and warpage risk. After T0/T1 trials, verify dimensions, flatness, snap-fit clearance and sealing surfaces through First Article Inspection (FAI). For complex or tight-tolerance assemblies, request a DFM review to check wall thickness, gate location, shrinkage allowance, tolerance targets and inspection method before steel cut.

Summary: How to Use Plastic Resin Shrinkage Data Correctly

Injection molding shrinkage DFM review before steel cut with mold steel allowance and inspection planning

Use plastic resin shrinkage data as an engineering reference, not as a final tooling value. ABS, PC, PMMA and PS usually shrink less, while PP, PE, POM, Nylon and PBT usually shrink more. Glass-filled grades such as PA66-GF30 and PBT-GF30 can reduce total shrinkage but create directional shrinkage and warpage risk. Final shrinkage assumptions should be confirmed with resin datasheets, DFM review, Moldflow analysis, process window control, T0/T1 tool trial samples, FAI, CMM or fixture inspection when CTQ dimensions, mating fit, flatness or sealing surfaces are involved.

Recommended Next Step for Engineers

Send your 2D drawing, 3D CAD, target resin grade, CTQ dimensions, tolerance requirements, surface finish, assembly fit requirements, application environment and expected production volume. Our engineering team can review shrinkage rate, mold steel allowance, wall thickness, gate location, flow direction, cooling balance, warpage risk and inspection requirements before cavity steel dimensions are finalized.

Engineering Review Output: The review can identify resin suitability, local shrinkage risk, cavity allowance concerns, wall-thickness uniformity issues, gate location risk, cooling imbalance, Moldflow or tool trial validation needs, CTQ inspection method, CMM / FAI requirements and possible production approval risks before steel cut.

Send Drawing for Shrinkage & DFM Review Review Injection Molding Material Selection Guide

FAQ: Plastic Resin Shrinkage Rate

What plastic has the lowest shrinkage rate?

Amorphous plastics such as ABS, PC, PMMA and PS usually have the lowest shrinkage rates among common injection molding materials. Typical shrinkage ranges are often around 0.3%–0.7%, depending on resin grade, wall thickness, gate location, packing pressure, mold temperature and cooling balance.

What plastic has the highest shrinkage rate?

Semi-crystalline plastics such as PE, PP, POM and some unfilled Nylon grades usually have the highest shrinkage rates. LDPE and HDPE can shrink significantly, often up to 3.0%–3.5%, depending on density, resin grade, wall thickness, packing pressure, cooling time and cooling balance.

What is the shrinkage rate of ABS?

ABS typically has a shrinkage rate around 0.4%–0.7%. Because ABS usually has lower and more predictable shrinkage than semi-crystalline plastics, it is often used for electronic enclosures, appliance housings, cosmetic covers and mating parts. Final ABS shrinkage value still depends on grade, wall thickness, gate location, packing pressure and tool trial results.

What is the shrinkage rate of PC plastic?

PC, or polycarbonate, typically shrinks around 0.5%–0.7%. Because PC is often used for clear, impact-resistant or optical parts, gate stress, birefringence, residual stress and optical distortion should be reviewed. Use visual optical inspection, polariscope review or FAI when optical performance or dimensional evidence is required.

What is the shrinkage rate of Nylon?

Nylon shrinkage varies widely by grade. PA6 may shrink around 0.7%–2.2%, while PA66 may shrink around 1.0%–2.0%. Glass-filled Nylon grades such as PA66-GF30 often show lower total shrinkage, around 0.3%–0.8%, but fiber orientation can create directional shrinkage, twist and warpage. Nylon also absorbs moisture, so conditioning and post-molding dimensional checks may be required for tight-tolerance parts.

What is the shrinkage rate of polypropylene?

Polypropylene, or PP, typically has a shrinkage rate around 1.5%–2.2%. Because PP is semi-crystalline and has relatively high shrinkage, wall thickness, rib-to-wall ratio, gate location, packing pressure and cooling balance should be reviewed with Injection Molding Design Guidelines before tool steel is cut. For PP parts with large flat surfaces or sealing features, use Moldflow review, flatness inspection or CMM checks after tool trials.

What is the shrinkage rate of polyethylene?

Polyethylene resins are semi-crystalline plastics with high shrinkage. High-density polyethylene (HDPE) typically shrinks around 1.5%–3.0%, while low-density polyethylene (LDPE) typically ranges from 1.5%–3.5%. Final molded size depends on density, grade, wall thickness, gate location, packing pressure, mold temperature and cooling balance.

What is the shrinkage rate of POM or acetal?

POM, also called acetal, typically shrinks around 1.8%–2.5%. Because POM is often used for gears, bushings, sliding parts and low-friction mechanisms, review gear pitch, bore size, roundness, packing pressure and CMM inspection requirements. For POM gears, use CMM profile checks, gear gauge inspection or roundness checks after tool trials.

Does glass fiber reduce shrinkage?

Yes. Glass fiber usually reduces total shrinkage, but it can create anisotropic, directional shrinkage because fibers align with melt flow. This can increase twist, flatness variation, connector pitch drift or pin alignment risk. Use Moldflow analysis to review fiber orientation, gate location, flow direction and warpage before tooling.

Can shrinkage rate be used directly for mold design?

Shrinkage rate values can support early mold cavity sizing, but they should not be used alone as one fixed scaling factor across the entire tool. Practical mold steel compensation must evaluate resin grade, local geometry, wall transitions, gate location, packing pressure, cooling balance, CTQ dimensions and inspection method. For high-risk or tight-tolerance parts, verify the resin choice with DFM review, Moldflow analysis, T0/T1 samples, FAI, CMM or fixture inspection before cutting or approving cavity steel.

Technical Disclaimer: Shrinkage ranges in these FAQ answers are typical references only. Final shrinkage should be confirmed with the selected resin supplier datasheet, filler content, part geometry, gate location, molding conditions, inspection method and T0/T1 tool trial results.