GPPS and HIPS are both polystyrene resins, and both are sold as clear or white plastic pellets that run on the same injection molding, extrusion and thermoforming lines. On a datasheet they can look close. In the part, they behave very differently. This guide explains where each grade fits, what to compare on the datasheet, and what to ask your polymer resin supplier before you confirm an order.
What makes them different
GPPS (general-purpose polystyrene) is the unmodified homopolymer. It is amorphous, glass-clear and stiff, with high surface gloss and good dimensional stability. Its weakness is toughness: GPPS is brittle and cracks under impact or sharp bending.
HIPS (high-impact polystyrene) is polystyrene modified with polybutadiene rubber. The rubber forms small particles inside the polystyrene matrix that absorb impact energy. The result is a much tougher material, but the rubber phase scatters light, so HIPS is opaque or milky white rather than clear, and it gives up some stiffness and surface hardness.
In short: choose GPPS when you need clarity and rigidity, and HIPS when the part must survive drops, snapping, folding or assembly stress.
Typical applications
- GPPS: clear food containers and lids, disposable cups, cosmetic and display packaging, light diffusers, stationery, and extruded foam board (XPS insulation).
- HIPS: refrigerator liners and appliance housings, thermoformed dairy cups, toys, and printable sheet for signage and packaging inserts.
- GPPS/HIPS blends: many processors blend the two to balance stiffness, toughness and cost, for example in disposable cutlery and some thermoformed trays.
What to compare on the datasheet
When you compare GPPS and HIPS grades from different producers, check that the values were measured with the same test standard (ISO or ASTM) and under the same conditions. The most useful properties are:
- Melt flow rate (MFR), usually at 200 °C / 5 kg. Higher MFR fills thin walls and long flow paths more easily; lower MFR gives better melt strength for extrusion and thermoforming.
- Notched impact strength (Izod or Charpy). This is where HIPS separates from GPPS, and where HIPS grades differ most from each other.
- Tensile strength and flexural modulus, which show stiffness. GPPS is higher on both.
- Vicat softening temperature, important for parts that see warm food, dishwashers or hot storage.
- Environmental stress crack resistance (ESCR) for HIPS used in refrigerator liners or in contact with fats and oils. Not every HIPS grade is designed for this.
- Light transmission and haze for GPPS used in clear packaging.
Processing notes
Both resins process easily across a wide temperature window and normally do not need drying unless the pellets have picked up surface moisture in storage. GPPS parts can stress-crack if they are ejected with high residual stress, so mold temperature and ejection design matter more than with HIPS. For HIPS sheet, check melt strength and gloss requirements before choosing a high-flow injection grade for extrusion.
Questions to ask your supplier
- Is the grade intended for injection molding, sheet extrusion, foam or thermoforming?
- For food packaging: which food-contact compliance statement is available for the grade and the destination market?
- Can you share the TDS and MSDS before the order, and the COA for the shipped lot?
- Is the grade available in original factory packing, and what is the current lead time?
Full Trust supplies GPPS and HIPS polystyrene resin from Chinese and international producers. You can browse the current grades on our PS resin page, or send us your part and process and we will suggest grades to compare.
