PS is a resin used in plastics processing, in two distinct grades. This page covers what each does and a regulatory point worth knowing before specifying it for packaging.
What is it?
ASTM D4549 classifies PS into two grades: unmodified (crystal) polystyrene — transparent and rigid — and rubber-modified polystyrene, which trades some transparency for higher impact resistance.
Why should I use it?
- A grade for either priority — clarity or toughness — see the breakdown below.
- Foam packaging made from PS is subject to a real, uneven patchwork of regional restrictions — see Limitations.
How it’s used
In Plastics & Polymers, unmodified (crystal) PS is used where transparency and rigidity are the priority; rubber-modified PS is used where impact resistance matters more, at some cost to clarity — both classified under ASTM D4549.
Limitations — when it isn’t the right choice
- Expanded (foam) PS foodservice packaging faces a real, uneven regulatory landscape in the US. There is no single federal rule — instead, individual states have enacted their own bans; Washington State, for example, restricts expanded polystyrene foodservice packaging under its own state law. Whether foam PS packaging is permitted depends on the specific jurisdiction it’s sold into, not a single nationwide standard — this needs checking per market, not assuming.