Plastic resin pellets prepared for drying before injection molding

Raw technical resin pellets prepared and itemized for moisture extraction review inside an environmental preparation bay before tooling verification protocols.

Resin Drying Temperature and Time Chart for Injection Molding

Use this resin drying temperature and time chart to compare common injection molding materials by drying requirement, typical drying temperature, drying time, moisture sensitivity and defect risk. Review nylon, PC, ABS, PBT, PET, TPU, PPS, PEEK, PP, POM and other plastics before production to reduce splay, bubbles, silver streaks, hydrolysis, brittleness and surface defects.

This plastic resin drying chart is a practical processing reference for manufacturing engineers, tooling teams, quality engineers and sourcing teams, not a full material encyclopedia. Use it to check drying temperature, drying time, moisture sensitivity, dryer type, dew point and under-dried defect risk before RFQ, mold trial or production release. This chart is for early processing review only. Supplier datasheets should override this general drying table when exact grade data is available.

Material Selection Note: This page focuses on drying behavior. For broader resin screening beyond drying variables, use the Injection Molding Material Selection Matrix to compare material families by mechanical performance, heat resistance, molding risk and documentation needs before tooling.

Engineering Quick Answer: How to Use This Resin Drying Chart

Most hygroscopic resins should be dried before injection molding because absorbed moisture can cause splay, bubbles, silver streaks, hydrolysis, brittleness, reduced mechanical strength and poor surface finish. Nylon, PC, PBT, PET, TPU, PPS, PEEK and PEI usually need controlled drying. PP, PE and POM are less moisture-sensitive, but surface moisture or poor storage can still create molding defects. Final drying settings should follow the exact resin grade, supplier datasheet, dryer type, dew point, storage condition and production requirements.

What This Drying Requirements Chart Is For

This chart provides early processing reference values for drying temperature, drying time, moisture sensitivity and under-dried defect risk. It helps project engineers, quality teams and sourcing teams identify which resin families need controlled drying before RFQ, mold trial or production release.

Why Supplier Datasheets Overrule General Metrics

A polymer family name alone does not provide enough data for final drying settings. Fillers, glass fiber percentage, color masterbatch, stabilizers, regrind percentage and storage condition can change drying behavior. Manufacturer technical data sheets (TDS) define grade-specific drying temperature, drying time, target moisture level and processing limits. These values should override general drying chart averages.

Why Drying Risk Affects Early RFQ and Production Readiness

Drying requirements can affect production readiness, dryer availability, material handling and mold trial planning. Underestimating drying time or dew point control can lead to splay, bubbles, unstable material flow, higher scrap and delayed mold trial approval. Before RFQ or mold trial, confirming dryer type, drying time, dew point, storage condition, regrind percentage and cosmetic or structural defect risk helps reduce RFQ uncertainty and mold trial risk.

Which Resins Must Be Dried — and Which Usually Do Not

Drying requirements should not be approved by resin family name alone. Exact grade, filler content, supplier datasheet, storage condition, regrind percentage and dryer setup can change the drying requirement. Misclassifying a resin before production may lead to splay, bubbles, unstable flow, out-of-tolerance parts or reduced mechanical strength.

Resins That Usually Require Controlled Drying

Nylon (PA6/PA66) Polycarbonate (PC) PBT PET TPU PPS PEEK PEI LCP

These materials are commonly treated as hygroscopic resins because they absorb moisture and usually require controlled drying before molding. If these resins are not dried correctly, they may show splay, bubbles, hydrolysis, brittleness or reduced mechanical properties. For these grades, verify drying temperature, drying time, dryer type, dew point and target moisture level against the supplier datasheet before molding starts. For specialized polyamide benchmarking details, check our processing comparison on PA6 vs PA66 vs Glass-Filled Nylon.

Resins That May Need Drying Depending on Storage and Grade

ABS PC/ABS Blends PMMA SAN TPE

These materials may or may not need drying depending on exact grade, packaging condition, storage history and surface appearance requirements. A sealed material lot may process cleanly, while prolonged open-bag storage in a humid warehouse can increase surface moisture risk. If surface moisture is not checked, it may vaporize during molding and cause splay, silver streaks, haze or cosmetic defects on visible surfaces.

Resins That Usually Have Lower Moisture Sensitivity

Polypropylene (PP) Polyethylene (PE) POM (Acetal) Polystyrene (PS)

These materials are generally less moisture-sensitive because they do not absorb much internal moisture under normal storage conditions. However, material handling still matters because sudden temperature changes or cold-to-warm storage transfers can create surface condensation on pellets. Surface moisture from condensation, poor storage or cold-to-warm transfer should still be checked before molding as it can cause splay, bubbles or unstable processing.

Drying Temperature and Time Table by Resin Family

Plastic Resin Drying Chart for Common Injection Molding Materials

Use this drying table for early processing review only. Actual drying temperature and drying time should follow the resin supplier datasheet, exact grade, moisture condition, dryer type, dew point, open-bag storage time, regrind percentage, color masterbatch and production requirements. Checking these conditions helps reduce splay, bubbles, silver streaks, hydrolysis, brittleness, dimensional variation and surface defects during molding.

Drying Status Legend: "Required" means controlled drying is normally needed before molding; "Usually lower risk" means drying may still be needed when surface moisture, condensation or poor storage is present.

Resin Family Drying Needed? Typical Drying Temperature Typical Drying Time Moisture Sensitivity Main Risk If Under-Dried
ABS Often recommended 75–85 °C 2–4 hours Low to moderate Splay, silver streaks, poor surface finish
Polycarbonate (PC) Usually required 110–130 °C 3–4 hours High Silver streaks, bubbles, hydrolysis, impact loss
PC/ABS Usually recommended 80–100 °C 3–4 hours Moderate to high Splay, surface defects, reduced appearance quality
PA6 / PA66 Required 80–90 °C 4–8 hours High Bubbles, brittleness, property loss, dimensional variation
Glass-Filled Nylon Required 80–90 °C 4–8 hours High Splay, reduced mechanical strength, dimensional drift
PBT Required 110–130 °C 3–4 hours High Hydrolysis, brittleness, low impact strength
PET Required 120–160 °C 4–6 hours High Hydrolysis, poor mechanical properties, surface defects
TPU Usually required 80–110 °C 2–4 hours High Bubbles, splay, poor surface finish, elastic property loss
TPE Grade-dependent 60–90 °C 2–4 hours Low to moderate Bubbles, splay, surface issues
PMMA Usually recommended 70–90 °C 3–4 hours Moderate Bubbles, haze, optical defects
POM (Acetal) Usually lower risk 80–100 °C if needed 2–3 hours Low Surface moisture defects, unstable processing
Polypropylene (PP) Usually lower risk 70–90 °C if needed 1–2 hours Low Surface moisture, splay from condensation or storage
Polyethylene (PE) Usually lower risk 60–80 °C if needed 1–2 hours Low Surface moisture, contamination-related defects
PPS Usually required 120–150 °C 3–4 hours Moderate to high Surface defects, property variation, processing instability
PEEK Usually required 150–170 °C 3–4 hours Moderate to high Surface defects, property loss, processing variation
PEI Usually required 140–160 °C 4–6 hours High Splay, bubbles, property loss
LCP Usually required 120–150 °C 4–6 hours Moderate to high Surface defects, dimensional variation, surface haze

Processing note: These values are typical reference ranges, not final molding instructions. Supplier datasheets, exact grade data, dryer dew point, storage condition and target moisture limits should override this general drying table.

Moisture Targets, Dew Point and Handling Notes

Drying temperature and drying time are only part of resin moisture control. A material can still mold poorly if the dryer dew point is too high, hopper residence time is too short, the material was stored open for too long, or the regrind percentage is high. Review supplier TDS, target moisture limit, dryer dew point, hopper residence time, dryer maintenance, open-bag storage time and regrind percentage before mold trial or production release.

Why Dew Point Matters for Hygroscopic Resins

For hygroscopic plastics, a desiccant dryer with controlled dew point is often required because hot air alone may not remove moisture absorbed inside the resin. Nylon, PBT, PET, TPU, PPS, PEEK and PEI should be reviewed by dryer dew point, hopper residence time and supplier target moisture level. Many hygroscopic resins use low-dew-point desiccant drying, but the target should follow the supplier TDS and exact grade requirement. Before molding, check these process inputs:

Dryer dew point target from supplier TDS
Actual drying temperature
Drying time
Hopper fill level and material bed depth
Open-bag storage duration
Regrind percentage
Color masterbatch condition
Sufficient stable mass flow in hopper
Regular desiccant maintenance

Hot Air Dryer vs Desiccant Dryer

Hot air drying may be enough for some lower-risk materials or surface moisture. Desiccant drying is usually preferred for hygroscopic engineering plastics because low-dew-point air can remove absorbed moisture more effectively from the pellet interior. Use this table to compare common dryer types before process review:

Dryer Type Typical Use Case Processing Limitation
Hot Air Dryer Surface moisture removal, non-hygroscopic materials, short drying reviews. May not remove absorbed moisture from hygroscopic engineering resins.
Desiccant Dryer Nylon, PC, PBT, PET, TPU, PPS, PEEK, and PEI processing cycles. Requires dew point monitoring, sufficient residence time and regular desiccant maintenance.
Hopper Dryer Continuous point-of-use drying directly above the machine feed throat. Needs stable material flow and sufficient residence time in the hopper.
Vacuum Dryer Grade-specific drying review or shorter drying cycles when approved by supplier data. Requires supplier drying guidance and grade-specific process validation.

Open-Bag Storage, Regrind and Color Masterbatch

Open-bag material storage can increase moisture risk before molding because pellets are exposed to shop-floor humidity. Confirm whether the resin bag was opened, how long it stayed open, warehouse humidity exposure, regrind percentage and whether the color masterbatch carrier needs drying. Checking the base resin and masterbatch together helps reduce splay, silver streaks or unstable material flow during molding.

Resin drying equipment reviewed for dew point and moisture control in contemporary Chinese manufacturing environment

Modern documentary image showcasing functional Asian factory drying hopper detail, desiccant assets, and organized pellets in clean preparation bay before tooling routing validation loops.

Under-dried resin samples inspected for splay bubbles silver streaks and surface haze on clean engineering inspection table

Molded sample plaques, transparent window parts, and sectioned pieces inspected for splay, bubbles, and silver streaks using precision gauges on a dedicated engineering verification station in a clean modern production environment.

What Happens If the Resin Is Under-Dried?

Under-dried resin can affect both visible part quality and mechanical performance. Some moisture-related issues appear immediately as splay, bubbles or silver streaks, while others may appear later as brittleness, weak snap-fit retention, dimensional variation or reduced impact strength after assembly. Moisture-related issues should be checked by visual inspection, part section review, mechanical retesting, dimensional inspection and supplier TDS review before changing tooling.

Surface Defects from Under-Dried Resin

When residual moisture reaches the hot barrel, it can vaporize during melting and create gas marks in the molded part. As the melt flows through gates, ribs, bosses and thicker sections, moisture-related gas can appear as splay marks, silver streaks, bubbles, voids or surface haze. These defects may cause visible housings, display bezels or transparent windows made from PC, ABS, PC/ABS or PMMA to fail appearance requirements. When these defects appear, check drying temperature, drying time, dryer dew point, open-bag storage, melt temperature, venting and gate condition before changing the mold.

Mechanical Property Loss from Moisture

Moisture may reduce mechanical performance even when the molded surface looks acceptable. Under-dried resin may cause voids, local embrittlement, lower tensile strength, reduced elongation and lower notched impact toughness. High-stress features such as snap-fit arms, mounting clip roots, self-tapping screw bosses and alignment latches should be checked for cracking, brittle fracture and retention loss after molding. For structural features, confirm mechanical performance with tensile or impact testing when required, snap-fit retention checks, screw boss torque checks and functional assembly testing.

Hydrolysis Risk in Engineering Plastics

For moisture-sensitive engineering plastics such as PBT, PET, nylon and selected high-performance resins, residual moisture can increase hydrolysis risk at elevated melt temperatures. Hydrolysis may reduce molecular weight, lower impact strength and reduce tensile performance. A molded part may look acceptable on the surface but still need mechanical testing, functional assembly checks or material review when hydrolysis risk is suspected. When hydrolysis risk is suspected, review supplier TDS, drying record, melt temperature, barrel residence time, material lot history and mechanical test results.

Under-dried resin defects checked with molded samples and inspection tools

Modern documentary industrial photo showcasing functional engineering inspection of molded samples labeled for moisture defects, including splay, bubbles, and property loss verification steps.

Moisture-Related Defects and Property Loss

Moisture-related defects should not be diagnosed by appearance alone. Splay, bubbles, silver streaks and haze can look similar to defects caused by melt temperature, residence time, venting, contamination or material degradation. When moisture is suspected, review the drying record, dryer dew point, storage history, melt settings, mechanical performance and dimensional inspection results before changing the tool.

Use this under-dried resin defect table to connect visible defects with the drying and process inputs that should be checked before changing the mold or approving the material.

Under-Dried Resin Defect Table

Moisture Defect What It Looks Like Common High-Risk Resins What to Check Before Material Approval
Splay Marks Silver or white fan-like streaks near the gate or along the flow path. ABS, PC, PC/ABS, TPU, PMMA Check drying time, dryer temperature, dryer dew point, melt temperature, venting and gate condition.
Bubbles Small internal voids or localized gas pockets in thick-walled component sections. Nylon (PA6/PA66), TPU, PC, PET Verify resin moisture content, dryer dew point stability and hopper residence time.
Silver Streaks Bright streaks or elongated lines running along the melt flow direction. PC, PMMA, ABS, PC/ABS Check material moisture level, drying record, melt temperature and injection speed.
Voids Internal gaps or gas pockets in thick walls, ribs or heavy sections. Nylon, PET, PBT, TPU Check target moisture level, packing pressure, venting and wall thickness transitions.
Poor Gloss Dull, hazy or inconsistent finish on visible cosmetic surfaces. ABS, PC/ABS, PMMA, PC Check material storage history, drying cycle dew points and core tool temperature.
Brittleness Cracking along thin ribs, clips or bosses, or low retention during assembly. Nylon, PBT, PET, PC Check hydrolysis risk, drying record, dryer dew point and barrel residence time.
Property Loss Reduced tensile strength margins, lower elongation capacity, or diminished notched impact toughness. Nylon, PBT, PET, PEI, PEEK Run mechanical retesting on molded samples when required, and review supplier TDS, drying record and molding process record.
Dimensional Drift Dimensional change, unexpected warpage or out-of-tolerance fits. Nylon, Glass-Filled Nylon, PBT Measure resin moisture level, compare dry-as-molded and conditioned dimensions, and use CMM or fixture inspection when tolerance risk is present.
Surface Haze Cloudy appearance, reduced visual clarity or lower light transmission in clear windows. PMMA, PC, Clear Amorphous Resins Check pre-heat drying consistency, audit lot contamination variables, and verify melt temperature limits.

Engineering Troubleshooting Rule: Because moisture-related defects can look similar to shear burning, thermal degradation, material contamination or poor venting, review drying records together with melt temperature, residence time, injection speed, venting and material lot history before changing the mold.

When Drying Risk Should Change Your Material Decision

Drying burden can become a material selection issue when a resin looks suitable on the drawing but is difficult to control in production. If the required drying time, dryer type, dew point control, open-bag handling or scrap risk does not fit the production plan, review the material and process trade-off before RFQ, mold trial or production approval.

When Drying Burden Creates Production Risk

Drying risk should be reviewed early when the part has tight tolerance, cosmetic, optical, thin-wall or load-bearing features. High-risk parts include tight tolerance parts, transparent or optical parts, high-gloss cosmetic surfaces and thin-wall features. If the component uses loaded snap fits, mounting clips, high regrind content, glass-filled engineering plastics or high-temperature resins with long barrel residence time, under-drying may increase the risk of brittleness, cracking, dimensional drift or reduced retention. For these parts, check drying records, molded sample appearance, snap-fit retention, screw boss cracking, dimensional drift and CMM or fixture inspection results before approval.

When to Review Alternative Resins

Review an alternative resin family or grade when the required desiccant dryer is not available, the drying window is too narrow, the dew point cannot be maintained, or open-bag storage cannot be controlled. If open-bag storage cannot be controlled, the resin is highly sensitive to hydrolysis, or moisture-related scrap is likely, review a less moisture-sensitive resin family or a grade with a wider drying window. For broader resin screening beyond drying variables, use the Injection Molding Material Selection Matrix to compare material families by mechanical performance, heat resistance, molding risk and documentation needs before tooling.

When to Request DFM and Process-Risk Review

Drying parameters should be reviewed together with part geometry, tooling layout and process window during early DFM review. Review wall thickness, ribs, bosses, gate location, weld lines and venting together with drying risk to define a stable molding process. A DFM and process-risk review should check drying condition, melt temperature, barrel residence time, gate location, venting, surface finish, tolerance requirements and inspection needs before tooling or production release.

What to Send for Resin Drying and DFM Review

Drying problems are easier to prevent before tooling and molding trials than to fix after visible defects appear. Sourcing, quality and product development teams should send resin data, drying conditions, drawings, CAD files, tolerance requirements, surface finish requirements and inspection needs before RFQ or mold trial. This helps the engineering team check drying risk, moisture-related defects, part geometry and process feasibility before tooling or production release.

Material & Processing Data Required

To review whether the resin drying requirement fits available equipment, storage condition and production planning, provide these material and processing inputs:

  • Exact Resin Grade: Supplier grade name and material code.
  • Technical Data Sheet (TDS): Drying recommendations, processing limits and material properties.
  • Dryer Type: Hot air dryer, desiccant dryer or vacuum dryer.
  • Drying Conditions: Planned drying temperature, drying time, dryer dew point and target moisture level if available.
  • Storage History: Open-bag duration and warehouse humidity.
  • Regrind Percentage: Planned regrind percentage and handling limits.
  • Dryer Dew Point: Target dew point from supplier TDS or drying plan.
  • Target Moisture Level: Supplier moisture limit if available.
  • Color Masterbatch: Carrier type and drying requirement.
  • Known Molding Defects: Splay, bubbles, silver streaks, haze, brittleness or dimensional drift.

Drawing & Geometric Files Required

To review wall thickness, ribs, bosses, gate location, weld lines, tolerance risk and surface requirements, include these drawing and geometry files:

  • 3D CAD Models: STEP, IGES, or native part files.
  • 2D Engineering Drawing: Current revision prints.
  • Tolerance Requirements: Critical dimensions, fit areas and inspection points.
  • Surface Finish Requirements: Texture, gloss, haze and visible appearance limits.
  • Inspection Requirements: FAI, CMM or PPAP requirements.
  • Wall Thickness: Nominal wall, thick sections, ribs and bosses.
  • Gate / Venting Concerns: Known gate, weld line, trapped air or cosmetic surface concerns.
  • Annual Volume: Expected production quantity and molding run plan.

Before mold trial or resin order approval, request a DFM & Engineering Review to check drying condition, hopper residence time, gate location, venting, surface finish, tolerance risk and inspection needs for moisture-sensitive molded parts. The review can also define whether FAI, CMM inspection or PPAP documentation is needed for production approval.

FAQ: Resin Drying Requirements for Injection Molding

Which resins need drying before injection molding?

Hygroscopic resins such as nylon, PC, PBT, PET, TPU, PPS, PEEK and PEI usually need controlled drying before injection molding. ABS, PMMA and PC/ABS may also need drying depending on grade and storage condition. PP, PE and POM are less moisture-sensitive but should still be checked for surface moisture. Final drying settings should follow the exact resin grade and supplier datasheet.

Do PP and PE need drying before injection molding?

PP and PE are generally less moisture-sensitive than hygroscopic engineering plastics. However, surface moisture from storage, condensation or poor packaging can still create molding defects, so material condition should be checked before production.

What happens if nylon is not dried before molding?

Undried nylon may show splay, bubbles, brittleness, reduced mechanical strength, dimensional variation and poor surface finish. PA6, PA66 and glass-filled nylon should be dried according to the exact grade datasheet, especially when the part is structural, tight-tolerance or load-bearing. For detailed material comparisons, see our guide on PA6 vs PA66 vs Glass-Filled Nylon.

Is hot air drying enough for all plastic resins?

No. Hot air drying may remove surface moisture, but many hygroscopic plastics require desiccant drying with controlled dew point. Nylon, PBT, PET, TPU, PPS, PEEK and PEI often require more controlled drying than hot air alone can provide.

Can plastic resin be over-dried?

Some resins can be damaged by excessive drying temperature or long residence time. Over-drying may cause discoloration, brittleness, degradation or processing instability. Drying settings should follow the supplier datasheet and actual dryer condition.

How do I know if a molding defect is caused by moisture?

Moisture-related defects may appear as splay, silver streaks, bubbles, voids, poor gloss, haze or brittleness. Similar defects can also come from melt temperature, residence time, venting, contamination or shear, so review the drying record, dryer dew point, storage history, melt settings and material lot history before changing the mold.

What dew point is needed for resin drying?

Many hygroscopic resins require desiccant drying with controlled low-dew-point air. The exact dew point should follow the resin supplier datasheet and exact grade requirement. Nylon, PBT, PET, TPU, PPS, PEEK and PEI often need tighter moisture control than hot air drying can provide.

Can I use the same drying time for all grades in one resin family?

No. Different grades in the same resin family may require different drying settings because glass fiber content, fillers, color masterbatch, stabilizers, regrind percentage and storage condition can change moisture behavior. Final drying temperature and drying time should follow the exact supplier TDS.

Need Resin Drying and DFM Review Before Production?

Send the exact resin grade, supplier datasheet, dryer type, drying temperature, drying time, dryer dew point, target moisture level if available, storage history, regrind percentage, known molding defects, 2D drawing, 3D CAD, tolerance requirement, surface finish requirement and inspection needs. Our engineering team can review drying risk, moisture-related defects, material feasibility, molded-in stress, tooling risk, FAI, CMM inspection and PPAP documentation needs before mold trial or production release.

Request Resin Drying Review

You can send incomplete data first. We will help identify missing resin grade, TDS, drying data, drawing details and inspection information before RFQ or production molding.