Splay shows up as silver streaks or a frosted, fan-shaped pattern on the surface of a molded part, usually pointing away from the gate. It almost always comes from gas in the melt. The question is where the gas comes from.
The usual causes
| Cause | How to tell | Fix |
|---|---|---|
| Moisture (most common) | Happens with nylon, PC, PET, PBT, ABS, PC/ABS, acrylic, TPU or PLA. Worse after humid days or a dryer problem. | Dry to the resin’s spec in a desiccant (dew-point) dryer and check moisture before molding. See the drying guide. |
| Overheating | Gets worse with longer cycles, higher melt temps or a barrel that’s too big for the shot. | Lower melt temperature, reduce residence time, check heater bands. |
| Trapped air | Splay near the gate or at the start of fill; changes with injection speed. | Adjust decompression and screw recovery; check venting. |
| Volatiles in the material | Follows a specific lot, regrind or additive package. | Check the COA, cut regrind percentage, or change to a cleaner lot or grade. |
When it’s the material
If you’re drying properly and running a normal process and still get splay, look at the resin itself: high regrind content, an additive that outgasses, or material that sat open and absorbed more moisture than your dryer can pull out. Some grades are simply more forgiving than others.
Related
Resin drying temperatures and times · Nylon · Polycarbonate · Tell us the grade you run now →