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Glass Fiber 10%, 20%, and 30% in Injection Molding

Glass Fiber 10%, 20%, and 30% in Injection Molding

Glass fiber raises modulus and heat deflection in PA, PBT, ABS, and other bases, but it also changes shrink, warp, and cosmetic behavior.

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Glass Fiber 10%, 20%, and 30% in Injection Molding

Pick a glass loading, not only glass filled

Buyers use GF10, GF20, and GF30 suffixes every day. Each step up trades toughness and surface quality for stiffness.

Glass fiber raises modulus and heat deflection in PA, PBT, ABS, and other bases, but it also changes shrink, warp, and cosmetic behavior.

Writing only glass filled nylon on a PO leaves the molder guessing whether you need GF10 for a clip or GF30 for a bracket.

This guide explains what to specify at each loading band and when to open a DFM review before T1.

Three identical black nylon L-brackets on a light gray studio surface labeled GF10 GF20 GF30 showing increasing stiffness loo

When to specify it

GF loading checklist

Use this on RFQs and BOMs before you lock a filled grade.

  • State base resin and exact GF percent (for example PA66-GF30).

  • Mark cosmetic faces that cannot show fiber read-through.

  • Note warp-critical dimensions and gate location if known.

  • Link to first-article inspection for filled grades.

Trade-offs

10% vs 20% vs 30% glass (qualitative)

Qualitative matrix. Confirm numbers on the supplier datasheet.

LoadingStiffness / heatImpact / surfaceTypical use
GF10Moderate boostBest surface of the threeClips, small brackets
GF20Balanced structuralSome fiber show on glossStructural housings
GF30Highest stiffnessWarp and wear risk riseMetal replacement brackets

Routing

Unfilled vs glass filled

Fill when stiffness or heat needs it, not by default.

Unfilled resin

  • Higher impact on many bases
  • Easier cosmetics
  • Lower mold wear on polish

Glass filled resin

  • Higher stiffness and heat
  • Anisotropic shrink
  • May need warp review

RFQ

What to write on the purchase order

Clear resin callouts reduce quote iterations and T1 surprises.

  1. 1

    Name the suffix

    Write PA66-GF30, not nylon with glass.

  2. 2

    Attach datasheet

    Supplier TDS sets drying and processing window.

  3. 3

    Flag cosmetics

    SPI finish and texture on filled grades need alignment.

  4. 4

    Plan T1 review

    Measure warp-sensitive dims on conditioned parts.

FAQ

FAQ

Does higher GF always mean stronger?

It raises stiffness and heat; impact can drop versus unfilled.

Can I switch from GF20 to GF30 in the same mold?

Only after validation; shrink and warp change.

Where do I learn surface streak risks?

See the glass-filled surface streaks article in the material risks series.

Related guides

Materials, comparisons, and risks

Internal links only render in cards and CTA blocks.

Next step

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Glass Fiber 10%, 20%, and 30% in Injection Molding | NetProto