Key Metrics for Reinforced Flame-Retardant PC: Choosing Between GF10 and GF20

Stiffness scales linearly, impact may not

Moving from 10% to 20% glass typically lifts flexural modulus from about 3,500 MPa to above 5,500 MPa with tensile strength rising in step. Notched impact, however, often rises slightly then falls back — fibre ends act as stress concentrators and orientation in thin walls creates anisotropy.

GF20 is therefore not a blanket upgrade over GF10. Where the dominant failure mode is drop impact or assembly stress, GF10 is frequently the safer choice.

Anisotropy and warpage

Higher glass content widens the shrinkage difference between flow and cross-flow directions, raising warpage risk. Flat covers and plates often need tool compensation or gate repositioning at GF20.

This is another reason to share the part drawing or dimension chain with your supplier rather than just a resin abbreviation.

Keeping flame retardance stable

Glass fibre itself is not easily flammable, but it creates a candlewick effect: fibres conduct the material into the flame zone and weaken FR performance. Reinforced FR PC therefore usually needs higher flame-retardant loading than unreinforced grades, or an anti-drip agent — typically PTFE.

Confirm the rating at your actual test thickness; do not assume reinforcement improves flame behaviour.