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Polystyrene (PS)

General-purpose polystyrene (PS) is a cheap, rigid, optically clear plastic that is easy to mold but inherently brittle, with only about 2% elongation. At roughly 45 MPa tensile and the lowest cost tier, it suits disposable and cosmetic parts where rigidity and clarity matter more than impact strength.

How Polystyrene (PS) machines

Rated 3/5. It cuts cleanly but its brittleness invites chipping and cracking, so sharp tools, light cuts, and careful support are essential. Heat from cutting can also craze or melt it. PS is far more commonly molded than machined given its low cost and easy flow.

Manufacturing & processing

Injection molded and extruded into sheet and foam with excellent flow and crisp detail reproduction. It is one of the easiest plastics to mold. Solvent bonding is simple. Its 70 C service ceiling and brittleness limit it to light-duty, room-temperature uses.

Typical applications

Disposable cutlery and cups, CD cases, cosmetic and packaging housings, models, and, as expanded foam, insulation and protective packaging. Clear GPPS is used for display boxes and lab labware where rigidity and transparency outweigh durability.

When to choose it

Choose PS when cost, rigidity, and clarity dominate and impact loading is minimal. If parts will be dropped, flexed, or handled roughly, step up to high-impact polystyrene, ABS, or SAN. Watch for crazing from solvents, oils, and stress, which cracks PS over time.

Suitable surface finishes

Common finishes for Polystyrene (PS): bead blasting, powder coating. Use the finish selector →

FAQ

Why is polystyrene so brittle?
General-purpose PS has a rigid, glassy amorphous structure with very low elongation, about 2%, so it cannot absorb impact and cracks instead. Adding rubber gives high-impact polystyrene (HIPS), trading some clarity and stiffness for toughness. Choose HIPS or ABS whenever drops or flexing are expected.
What is crazing and how do I avoid it?
Crazing is the network of fine cracks PS develops under stress, especially when exposed to certain solvents, oils, or cleaners. Avoid it by minimizing molded-in and assembly stress, keeping incompatible chemicals away, and selecting a tougher grade or different polymer if the part faces solvents or sustained load.
How does SAN differ from plain polystyrene?
SAN copolymerizes styrene with acrylonitrile, giving better stiffness, heat resistance, chemical resistance, and clarity than PS while remaining brittle. If you like PS's clarity and rigidity but need more durability and chemical tolerance, SAN is a logical step up, still well below ABS in toughness.

Property values are typical/nominal for early guidance and vary by temper, grade, supplier and heat treatment. Confirm critical specs against a certified datasheet or with an mfgiq engineer.