The short answer
Glass fill is reinforcement: it raises strength, stiffness and heat resistance a lot, but can cause warp and a rougher surface. Mineral fill mainly adds stiffness and flatness at lower cost, with less effect on strength. Glass-mineral blends balance the two.
Fillers change a base resin more than almost anything else. Choosing between glass and mineral comes down to whether the part needs strength and heat, or flatness, stiffness and cost.
Side by side
| Property | Glass-filled | Mineral-filled |
|---|---|---|
| Main purpose | Reinforcement: strength, stiffness, heat | Stiffness, flatness, lower cost |
| Tensile strength | Large increase | Little change; can decrease (especially calcium carbonate) |
| Stiffness | Large increase | Moderate increase |
| Heat deflection | Large increase | Moderate increase |
| Warp | Higher; shrinkage differs along and across flow | Lower; shrinkage more even |
| Impact strength | In nylon and PP often holds or improves notched impact; in already tough resins like PC it usually lowers it | Often lowers impact |
| Surface finish | Fibers can show | Smoother |
| Tool wear | Higher (abrasive) | Lower to moderate |
| Relative cost | Higher | Lower |
| Common examples | PA66 GF30, PBT GF30, PP GF30, PPS GF40 | Talc-filled PP, mineral-filled nylon, calcium carbonate PE |
General trends at similar filler levels; exact effects depend on the base resin, filler type, coupling and level.
Why glass-filled parts warp
Glass fibers line up with the flow of the melt. The part shrinks less along the fibers than across them, so flat or long parts can bow or twist. Mineral particles are more uniform and shrink more evenly. Moving the gate, adding mineral, or switching to a glass-mineral grade are common fixes. See warped parts.
Choose glass-filled when
- The part carries load or must resist creep
- It runs hot and needs higher heat deflection
- Metal replacement or structural brackets
- Fatigue or impact under load matters
Choose mineral-filled when
- Flatness and low warp matter most
- You need more stiffness at low cost
- A smoother, more even surface is needed
- Appliance panels, housings, automotive interior parts
Grades we source
We source glass-filled, mineral-filled and glass-mineral grades of PP, nylon, PBT, PPS and others, and custom compounding and color are available, with a COA on every lot, tested to ASTM or ISO methods. See glass-filled nylon, glass-filled PBT and custom compounding.
Common questions
What is the difference between glass-filled and mineral-filled plastic?
Glass fibers reinforce the plastic, raising strength, stiffness and heat resistance a lot. Mineral fillers such as talc, mica or calcium carbonate mainly add stiffness and reduce warp and cost, with a smaller effect on strength.
Which warps less, glass-filled or mineral-filled?
Mineral-filled, usually. Glass fibers line up with the flow and shrink differently along and across it, which causes warp. Mineral particles are more uniform, so shrinkage is more even.
Is mineral-filled plastic cheaper?
Usually. Mineral fillers are inexpensive and can replace some of the polymer. Talc-filled PP is one of the most common low-cost stiff compounds.
Can you combine glass and mineral fillers?
Yes. Glass-mineral grades balance strength with lower warp and better surface, and are common in nylon and PP for housings and flat parts.
Does glass fill hurt the surface finish?
It can. Glass fibers can show at the surface, especially with cold molds. Mineral fill usually gives a smoother, more even surface.
Tell us the filled grade you run now
A polymer chemist reviews every request, then matches your grade or finds a qualified equivalent and prices it.
What to send for an accurate quote
- The grade name, from any supplier, or a data sheet
- Color (natural, black or a custom match)
- Fill type and percentage, if any
- Melt flow, if you know it
- Quantity for this order and what you use in a year
- Ship-to city and state or province