Technical Reference

Plastic Resin Shrinkage Rate Chart for Injection Molding

Plastic resin shrinkage rate chart with resin samples and molded part inspection samples

Compare typical plastic resin shrinkage rates for ABS, PC, Nylon, PP, PE, POM, PMMA, PBT and glass-filled resins. Use this injection molding shrinkage chart as an early reference for mold steel allowance, dimensional risk, warpage tendency and DFM review before tooling. Use this chart as an early reference only; final cavity steel dimensions should be confirmed with the selected resin datasheet, wall thickness review, processing window and tool trial results.

Quick Engineering Answer

Plastic resin shrinkage rate is the percentage a molded plastic part contracts as it cools after injection molding. Amorphous plastics such as ABS, PC and PMMA usually have lower shrinkage, while semi-crystalline plastics such as PP, PE, POM and Nylon often shrink more. Final shrinkage depends on resin grade, filler content, wall thickness, gate location, packing pressure, mold temperature, cooling balance and tool trial results.

To initiate an accurate shrinkage or warp risk assessment, send your 2D drawing, 3D CAD, target resin, tolerance definitions, surface finish criteria, and expected production volume. Our technical office can cross-check candidate polymer performance vectors via an advanced DFM review and comprehensive rheological path Moldflow analysis pri or to finalizing core layouts.

Send Drawing for Shrinkage & DFM Review Compare Resin Selection Matrix

Plastic Resin Shrinkage Rate Chart

Use this plastic resin shrinkage rate chart to compare common injection molding materials by shrinkage range, resin type, risk level and DFM concern. It covers ABS, PC, Nylon, PP, PE, POM, PMMA, PBT and glass-filled grades used for housings, connectors, gears, covers, clips and functional parts. Use these values as early design references only. Confirm final shrinkage data with the selected resin supplier datasheet, filler content, ASTM D955-style test conditions, part geometry and 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	Stable for housings, cosmetic covers and snap-fit features; review thick bosses and ribs for sink risk.
PC	Polycarbonate	0.50 – 0.70	Medium	Amorphous	Check gate stress, optical stress and residual stress; clear parts may require polariscope or visual optical inspection.
PC/ABS	PC ABS Blend	0.40 – 0.70	Low	Amorphous blend	Good for enclosure fit and cosmetic surfaces; review thick bosses, ribs and local sink risk.
PMMA	Acrylic	0.30 – 0.70	Low	Amorphous	Check optical clarity, gate stress and cracking risk; PMMA is brittle and may need controlled gate design and packing pressure.
PS	Polystyrene	0.40 – 0.70	Low	Amorphous	Low shrinkage but brittle; check structural performance and continuous flexural load constraints.
PP	Polypropylene	1.50 – 2.20	High	Semi-crystalline	High flatness and warpage risk; review wall thickness, gate location, packing pressure and cooling balance.
HDPE	High-Density Polyethylene	1.50 – 3.00	High	Semi-crystalline	Large shrinkage; check cavity allowance, wall thickness and cooling balance before tool steel sizing.
LDPE	Low-Density Polyethylene	1.50 – 3.50	High	Semi-crystalline	High shrinkage and flexible part deformation risk; keep wall thickness uniform and review ejection deformation.
POM	Acetal	1.80 – 2.50	High	Semi-crystalline	Check gear pitch accuracy, roundness, molded datum features and CMM inspection plan. Verify critical features via gear inspection toolings.
PA6	Nylon 6	0.70 – 2.20	High	Semi-crystalline	Moisture conditioning significantly affects dimensions. Review environmental exposure profiles during design and post-mold conditioning.
PA66	Nylon 66	1.00 – 2.00	High	Semi-crystalline	Review moisture absorption, conditioning requirements, shrinkage range and heat exposure barriers before tooling layouts lock.
PA66-GF30	Glass-Filled Nylon	0.30 – 0.80	Medium	Filled semi-crystalline	Lower total shrinkage but directional warpage risk. Always verify directional fiber alignment through advanced pre-tooling Moldflow analysis.
PBT	Polybutylene Terephthalate	1.20 – 2.00	Medium	Semi-crystalline	Common choice for connector bodies; check pitch tolerances and terminal pin clearance bounds using customized inspection fixtures.
PET	Polyethylene Terephthalate	1.20 – 2.00	Medium	Semi-crystalline	Dew-point drying prerequisites and active tool skin crystallization thresholds must be tightly regulated during continuous processing.
TPU	Thermoplastic Polyurethane	0.80 – 2.00	Medium	Elastomer	Shrinkage tracks closely with localized durometer hardness parameters. Check overmolding bond mating geometry interfaces.
TPE	Thermoplastic Elastomer	1.00 – 2.50	High	Elastomer	Evaluate substrate material pairings, flow lengths, and part ejection deflection risks within active overmolding layout zones.
PPS	Polyphenylene Sulfide	0.60 – 1.50	Medium	High-temp semi-crystalline	Filled grades may require fiber orientation and warpage review before steel cut to secure critical concentricity bounds.
PEI	Polyetherimide	0.50 – 0.80	Medium	High-temp amorphous	Good dimensional stability for high-temperature applications; review mold temperature and tooling requirements.
PEEK	Polyetheretherketone	1.00 – 1.50	Medium	High-temp semi-crystalline	Requires high-temperature tooling, controlled mold temperature and a stable processing window to prevent volumetric contraction deviations.

Engineering Notice: Shrinkage ranges should be verified against resin supplier datasheets, ASTM D955-style test data, ISO test conditions, filler content, part geometry, processing window and T0/T1 tool trial results. For live projects, confirm shrinkage assumptions with an active DFM review before finalizing cavity steel dimensions and tool layout.

What Is Shrinkage Rate in Injection Molding?

Shrinkage-Affected CTQ Features

Plastic shrinkage affects critical-to-quality (CTQ) dimensions. Tooling engineers should review shrinkage risk on these features:

Wall thickness, ribs and boss areas with sink risk
Snap-fit, sealing and mating-part clearance
Sink, void and flatness risk around thick sections
Flatness areas, pin alignment features and gear or roundness requirements

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. Plastic shrinkage affects mold steel allowance, part tolerance, flatness, snap-fit clearance, sealing surfaces and assembly fit. This value should be reviewed during DFM, tool trial and inspection planning because shrinkage affects cavity steel allowance, CTQ dimensions and final assembly fit. Shrinkage values should be checked against the selected resin supplier datasheet, ASTM D955-style test data, part geometry, processing window 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 usually offset to account 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 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; final shrinkage changes with material grade, filler content, wall thickness, gate location, packing pressure, mold temperature, cooling time and cavity balance. For high-shrinkage, glass-filled, thin-wall or large flat parts, use Moldflow analysis before tooling to review fill balance, packing behavior, cooling imbalance and warpage risk. Use Moldflow analysis when the part has high-shrinkage resin, glass-filled material, thin walls, long flow length, large flat surfaces, tight tolerance or multi-cavity tooling.

Why Some Plastic Resins Shrink More Than Others

Plastic resin shrinkage comparison for amorphous crystalline and glass-filled samples

Different plastic resins shrink at different rates because their molecular structure, crystallinity, filler content and cooling behavior are different. This is why ABS, PC and PMMA usually behave differently from PP, PE, POM, Nylon and PBT during injection molding. Reviewing these material differences before cavity sizing helps reduce tolerance drift after molding.

Separating amorphous, semi-crystalline and filled resins helps tooling teams review shrinkage allowance, runner balance, gate location and cooling layout before mold steel is finalized. For complex or high-risk features, compare shrinkage data with the Injection Molding Material Selection Guide before selecting the final resin. Final shrinkage still depends on the processing window, packing pressure, mold temperature, cooling balance and 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. They are often used for housings, cosmetic covers, clear parts and snap-fit features where dimensional stability and surface appearance matter. Gate stress, sink marks and packing still need to be reviewed.

In a plastic shrinkage rate table, ABS and PC usually show lower shrinkage than PP, PE, POM and Nylon, but gate stress, wall thickness and packing still affect final molded dimensions. For PMMA clear parts, check shrinkage, gate stress and residual stress before finalizing cavity steel and polishing requirements. For clear PC or PMMA parts, use optical inspection or polariscope review when gate stress or residual stress is critical.

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

Semi-crystalline plastics such as PP, PE, POM, Nylon and PBT usually have higher shrinkage because crystallization creates additional volume change during cooling. These materials often require closer DFM review for flatness, sealing surfaces, long flow paths, ribs, bosses and assembly features.

PP and PE usually require closer review because higher shrinkage can affect flatness, sealing surfaces and cavity steel allowance. POM, Nylon and PBT also need review of flow direction, cooling balance, wall transitions and CTQ dimensions before steel offsets are locked. Use Injection Molding Design Guidelines to review wall thickness, ribs, bosses, gate location and cooling balance when semi-crystalline resins are used. For PP, PE, POM, Nylon and PBT parts with flatness or assembly risk, use Moldflow review, flatness inspection and FAI after tool trials.

Glass-Filled Resins and Directional Shrinkage

Glass-filled resins such as PA66-GF30, PBT-GF and PPS-GF usually show lower total shrinkage than unfilled grades, but fiber orientation can create directional shrinkage. This is important for connector housings, pin alignment, flatness, clips and structural parts where flow-direction and cross-flow shrinkage behave differently.

Glass-filled nylon shrinkage should be treated as a typical range, not an exact value, because fiber orientation can change flatness and pin alignment. Use Moldflow analysis to review gate location, fiber orientation and warpage risk before finalizing the tool layout. For glass-filled connector housings, validate pin alignment, datum features and flatness with fixture inspection or CMM after tool trials.

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

The most common shrinkage questions compare ABS, PC, Nylon, PP, PE and POM because these resins are frequently used for molded housings, gears, connectors, covers, clips and mechanical parts. The table below compares low-shrinkage amorphous plastics such as ABS and PC with higher-shrinkage semi-crystalline plastics such as PP, PE, POM and Nylon and their main DFM risks.

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

Material	Shrinkage Behavior	Better For	Watch Out For
ABS	Low, typically 0.40 – 0.70%	Housings, covers, cosmetic parts	Sink around thick bosses and ribs
PC	Low to medium, typically 0.50 – 0.70%	Clear and impact-resistant parts	Gate stress, birefringence, optical distortion
Nylon	Medium to high, grade-dependent, typically 0.70 – 2.20%	Structural and wear-resistant parts	Moisture absorption and dimensional drift
PP	High, typically 1.50 – 2.20%	Living hinges, chemical resistance, lightweight parts	Warpage, flatness and shrinkage mismatch
PE	High, typically 1.50 – 3.50%	Chemical-resistant or flexible parts	Large cavity allowance and cooling variation
POM	High, typically 1.80 – 2.50%	Gears, sliding parts, precision mechanisms	Roundness, pitch accuracy and shrink drift

Which Plastic Has the Lowest Shrinkage?

ABS, PC, PMMA and PS usually have lower shrinkage than PP, PE, POM and Nylon. These amorphous plastics are often preferred when part fit, cosmetic surface and dimensional consistency are important.

Final shrinkage still depends on resin grade, part geometry, wall thickness, gate location and molding conditions. For mating clearances, snap-fits or sealing surfaces, review CTQ features 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 higher plastic shrinkage rates. These materials can work well for chemical resistance, living hinges, wear resistance or mechanical function, but they require closer review of wall thickness, cooling balance, gate location and inspection method.

For high-shrinkage semi-crystalline resins, review wall thickness, gate location and cooling balance with the Material Selection Guide, then use Moldflow analysis, flatness fixture, CMM or FAI when dimensional risk is high. For PP, PE, POM and Nylon parts with flatness, roundness or assembly risk, dimensional validation after tool trials is essential.

How Shrinkage Rate Affects Mold Steel Dimensions

Injection mold cavities are often designed larger than the final plastic part because the resin contracts during cooling. Real molded part dimensions depend on local geometry, wall transitions, ribs, bosses, packing, cooling, gate location, CTQ features and resin flow direction. Shrinkage rate helps estimate cavity steel allowance, but final offsets should be confirmed with DFM, Moldflow and tool trial inspection.

Injection Mold Shrinkage Allowance

Injection mold shrinkage allowance is the cavity size compensation used to account for expected plastic contraction. For low-shrinkage resins such as ABS or PC, the allowance is usually smaller and more predictable.

For high-shrinkage resins such as PP, PE, POM and Nylon, review cavity offsets, wall thickness, ribs, bosses, gate location and cooling layout with Injection Molding Design Guidelines before steel cut. Shrinkage allowance should be treated as an early cavity sizing reference and confirmed with resin datasheet values, CTQ dimension review 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 and pack differently. Thick bosses, ribs, long flow paths, flat sealing surfaces and thin-wall sections may shrink at different rates.

CTQ dimensions should be reviewed separately during DFM review and tool layout planning before cavity steel dimensions are finalized. Review snap-fit clearance, sealing surfaces, pin alignment, gear pitch, 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 layout and packing conditions before finalizing cavity steel dimensions.

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

Engineering Note

Mold steel dimensions should use shrinkage data as an early reference only. Review flow direction, wall transitions, ribs, bosses, gate location, cooling layout and CTQ dimensions. For high-shrinkage or glass-filled resins, use Moldflow validation, FAI, CMM or fixture checks to verify cavity offsets before production approval. For CTQ features, verify molded dimensions with FAI, CMM, flatness fixture, cavity-to-cavity comparison or functional gauges after tool trials.

Shrinkage Risk by Part Geometry

Plastic shrinkage risk is not only a material issue. The same resin can behave differently depending on wall thickness, flow length, ribs, bosses, gates, flat surfaces and assembly features. A shrinkage rate chart should be used together with geometry review, DFM review and inspection planning.

Injection Molding Shrinkage Risk Matrix

Part Geometry	Shrinkage Risk	Typical Result	Recommended Review
Thick boss	Local sink and void	Weak screw post	DFM wall review
Long flat cover	Bowing / warpage	Assembly mismatch	Moldflow + flatness check
Snap-fit housing	Clearance drift	Loose or tight fit	FAI + CMM check
Connector housing	Pin alignment error	Terminal mismatch	Terminal gauge, datum fixture or CMM datum check
Gear	Pitch and roundness error	Noise / wear	CMM profile check, gear gauge or pitch inspection
Clear lens	Optical stress	Birefringence	Polariscope review, visual optical inspection and gate-area check
Multi-cavity part	Cavity-to-cavity variation	Inconsistent fit	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, connectors and transparent optical surfaces. Before mold steel dimensions are finalized, review these features for wall uniformity, gate location, cooling balance, packing access, ejection risk 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 material or geometry creates dimensional risk. A resin shrinkage chart can identify early risk points, but high-risk parts should be reviewed with DFM, Moldflow and inspection planning before tool steel is cut.

DFM and Moldflow Trigger Table

Condition	Why It Matters	Recommended Action
Shrinkage > 1.2%	Higher risk of dimensional drift across wall transitions and CTQ features	DFM review + Moldflow analysis
Glass-filled resin	Fiber orientation can create directional shrinkage, twist and warpage	Moldflow fiber-orientation review before gate location and tool layout are finalized
Tight tolerance	Small dimensional errors can affect assembly fit, sealing 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 and flatness variation	Review gate location and cooling balance, then verify flatness with a fixture or CMM after tool trials
Multi-cavity mold	Fill balance, packing pressure and cavity-to-cavity dimensional variation	Use runner balance review, cavity-to-cavity FAI and process window check to control dimensional variation
Clear part	Gate stress and residual stress can create birefringence, haze or optical distortion	Use gate location review, packing pressure control, polariscope review and visual optical inspection
Connector	Terminal pin alignment deviations compromising mating clearances	Terminal gauge, datum fixture and CMM datum check
Gear or round part	Pitch accuracy and out-of-roundness errors driving premature wear	CMM profile check, concentricity check and gear gauge inspection

Quick Answer: When Is Moldflow Needed for Shrinkage?

Quick Engineering Answer

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

Common Mistakes When Using a Shrinkage Rate Chart

Common issues occur when teams ignore part geometry, processing window, filler content, fiber orientation and validation methods such as Moldflow, FAI, CMM or fixture checks. Treating generic table indices as unalterable parameters without empirical checks often triggers costly downstream dimensional errors.

Treating Datasheet Shrinkage as Final Part Shrinkage

Resin datasheet shrinkage values are usually based on standard test plaques, supplier grade data and controlled molding conditions, not the final production geometry. A production molded part can shrink differently because of wall thickness transitions, gate location, packing pressure, cooling balance, flow direction and cavity-to-cavity variation.

Engineering Validation: Confirm datasheet shrinkage with the selected resin grade, ASTM D955-style test data, part geometry, processing window and T0/T1 tool trial samples.

Using One Shrinkage Value for the Entire Mold

Shrinkage patterns vary significantly across different features of the same part. Thick bosses, thin walls, ribs, flat sealing surfaces and long-flow sections can shrink at different rates. Critical-to-quality (CTQ) dimensions should be reviewed individually instead of applying one average shrinkage value across the entire mold cavity.

Engineering Validation: Verify CTQ dimensions with FAI, CMM, fixture checks and cavity-to-cavity comparison after tool trials before launching high-volume operations.

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 may reduce total shrinkage, but fiber orientation can increase directional shrinkage, twist and warpage; use Moldflow analysis before tooling when pin alignment, flatness or assembly fit is critical.

Engineering Validation: Use Moldflow analysis to review fiber orientation, gate location, warpage risk and pin alignment before tool layout is finalized.

Ignoring Mold Temperature and Packing Pressure

Melt temperature, mold temperature, packing pressure and cooling time can change final part dimensions. If the process window changes between tool trials and production, shrinkage-related dimensions can drift from drawing tolerances across deep features.

Engineering Validation: Use trial data, approved process window 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, flow length, cooling behavior, ejection force, surface finish and final molded dimensions. 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 and inspection plan before production approval is officially locked.

Inspection Methods for Shrinkage-Related Dimensional Risk

Shrinkage-related dimensional risk should be verified with appropriate inspection methods. The right method depends on whether tool trial samples show clearance, flatness, pin alignment, roundness, optical stress, CTQ feature or cavity-to-cavity variation risk.

Inspection Methods for Injection Molding Shrinkage Risk

Shrinkage-Related Risk	Inspection Method	Use Case
Snap-fit clearance drift	FAI / CMM	ABS, PC/ABS housings
Flatness change	Flatness fixture / CMM with datum reference	PP, POM, PA flat parts
Pin alignment error	Terminal gauge, datum fixture or CMM datum check	PA66-GF30 connectors
Roundness / pitch error	CMM profile / gear gauge or pitch inspection	POM gears
Optical stress	Polariscope review, visual optical inspection and gate-area check	PC / PMMA lenses
Cavity variation	Cavity balance review, cavity-to-cavity FAI and process window check	Multi-cavity molds
Sealing surface mismatch	CMM / leak fixture check	Covers, housings, fluid parts

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 drawing, datum scheme, cavity number and approved Scientific Molding process window. These inspection protocols support repeatable production and process stability before production approval.

Example: PP vs ABS Shrinkage Risk Before Tooling

PP and ABS shrinkage comparison for flatness and mating fit control

Note: This example scenario compares PP and ABS for a molded housing or cover before tooling. Final material choice should be confirmed with resin datasheets, DFM review and tool trial inspection. PP and ABS are often compared when teams need to balance chemical resistance, cost, surface appearance, living hinge function and dimensional stability. Engineering teams should review these material differences early because PP and ABS can require different shrinkage allowance, gate location, cooling balance and inspection plans.

Because ABS is amorphous and PP is semi-crystalline, engineers should review cavity allowance, gate location, wall thickness and cooling layout before steel cut. For alternative resin options, review the Injection Molding Material Selection Guide before final material approval.

PP Housing with Flatness Risk

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

PP usually has a higher shrinkage rate than ABS, so abrupt wall transitions, uneven ribs and large flat surfaces can increase flatness and warpage risk. Review wall thickness, rib layout, gate location and cooling balance before cavity steel dimensions are finalized. For wide PP covers, use Moldflow and flatness inspection when long flow length, uneven cooling, sealing surfaces or tight assembly fit are present.

ABS Housing with Dimensional Fit Requirement

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

Because ABS is amorphous, it usually has lower and more predictable shrinkage than PP, but cavity offsets still depend on wall thickness, gate location, packing and tool trial results. This can help maintain snap-fit clearance, mating fit and cosmetic surface stability when bosses and ribs are reviewed during DFM. ABS usually has lower shrinkage than PP, but final snap-fit clearance, sealing surfaces and mating features should still be checked with FAI, CMM or fixture inspection after T0/T1 trials. Sourcing and engineering teams can use the Injection Molding Material Selection Matrix to compare alternative amorphous grades before final material approval.

Recommended Validation Method

For PP, use Moldflow and flatness inspection when large surfaces or uneven ribs are present. For ABS, use FAI, CMM or fixture checks on snap-fit clearance, sealing surfaces and mating features. In both cases, final shrinkage should be confirmed through tool trial samples.

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 PP, verify fill balance, cooling imbalance, flatness and warpage risk. For ABS, verify snap-fit clearance, boss sink, sealing surfaces and cosmetic fit. 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 and DFM review before steel cut

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 can reduce total shrinkage but create directional shrinkage risk. For tight-tolerance, high-shrinkage or glass-filled parts, confirm the resin choice with DFM review, Moldflow analysis, inspection planning and tool trial sample validation before steel cut. Final shrinkage assumptions should be checked with tool trial samples, FAI, CMM or fixture inspection when CTQ dimensions, mating fit or sealing surfaces are involved.

Recommended Next Step for Engineers

Send your 2D drawing, 3D CAD, target resin, tolerance, surface finish, application and production volume. Our engineering team can review shrinkage rate, cavity allowance, wall thickness, gate location, warpage risk and inspection requirements before cavity steel dimensions are finalized.

Engineering Review Output: The technical assessment systematically identifies plastic resin suitability, localized shrinkage risk ranges, cavity allowance concerns, wall-thickness uniformity issues, gate path or tool cooling system risks, and final downstream metrology or inspection requirements.

Send Your Drawing for Shrinkage & DFM Review Review the Injection Molding Material Selection Matrix

FAQ: Plastic Resin Shrinkage Rate

What plastic has the lowest shrinkage rate?

Amorphous plastics such as ABS, PC, PMMA and PS usually have lower shrinkage than semi-crystalline plastics. Typical shrinkage ranges are often around 0.3%–0.7%, depending on resin grade, wall thickness, gate location and molding conditions.

What plastic has the highest shrinkage rate?

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

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 or impact-resistant parts, gate stress, birefringence and optical distortion should be checked with visual optical inspection, polariscope review or FAI when required. For clear PC parts, review gate stress with visual optical inspection, polariscope review and gate-area dimensional checks when optical performance is critical.

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 usually show lower total shrinkage, around 0.3%–0.8%, but fiber orientation can increase directional shrinkage, twist and warpage risk. 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 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, part geometry, packing pressure 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, sliding parts and low-friction mechanisms, review gear pitch, 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 or connector pin alignment risk. Use Moldflow analysis to review fiber orientation, gate location and warpage before tooling.

Can shrinkage rate be used directly for mold design?

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

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, molding conditions and T0/T1 tool trial results.

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