Polystyrene family (GPPS, HIPS, SAN)

GPPS (General-Purpose Polystyrene)

Easy to process, low shrinkage, good dimensional stability. GPPS is transparent but brittle; HIPS is impact-resistant; SAN is chemical-resistant and transparent.

Processing temperatures

Melt (injection) temperature220 °C
Mold surface temperature40 °C
Ejection temperature80 °C

Typical values. They vary (±) with grade and manufacturer; see the data sheet.

Physical properties (typical)

Density1.05 g/cm³
Shrinkage (flow / cross)0.5 / 0.5 %
Specific heat1.3 kJ/kg·K
Thermal conductivity0.13 W/m·K

Drying

Usually not required (moisture control is good practice for SAN).

For exact conditions see the material data sheet. Drying guide →

Points to watch

  • Stress cracking (contact with solvents/oil)
  • GPPS is brittle, sharp corners crack

Typical use: Disposable items, packaging, household goods, appliance housings

Defects common with this material

Stress cracking

The part cracks during assembly, on contact with oil/solvent or over time; the crack usually starts at stressed areas.

stress crack · crack · environmental stress cracking

Weld line (knit line)

A line and a weak zone where two melt fronts meet.

weld line · knit line · joining line

Short shot (incomplete fill)

The cavity does not fill completely; the farthest or thinnest area of the part stays incomplete.

incomplete fill · underfill · non-fill

Flash

Plastic escapes through the parting line or around the ejector pins.

flash · overflow · parting line flash

Other grades in the same family

HIPS (High-Impact Polystyrene)

Amorphous220 °C melt · 45 °C mold

SAN

Amorphous235 °C melt · 60 °C mold

Do the values for this material not match your grade? and we will correct them.