PS (Polystyrene): Applications, Advantages & Injection Molding Guide

PS, or Polystyrene, is a widely used thermoplastic known for its clarity, rigidity, and ease of processing. It exists in various forms, such as general-purpose polystyrene (GPPS), high-impact polystyrene (HIPS), and expandable polystyrene (EPS), each offering unique benefits depending on the application.

What Is PS?
Polystyrene is an amorphous thermoplastic polymer derived from styrene monomer. GPPS is transparent and brittle, while HIPS includes rubber modifiers for better impact resistance. EPS is a foam form, commonly used in packaging and insulation.

Key Applications of PS
Polystyrene is used across consumer goods, food service, packaging, and electronics due to its light weight, formability, and cost efficiency.

Packaging & Food Service
– Disposable cutlery, cups, and plates
– Food containers and clamshells
– Protective packaging and foam trays

Consumer Goods
– CD/DVD cases and display products
– Cosmetic containers
– Toys and household items

Electronics
– TV and monitor housings
– Audio equipment and instrument panels
– Switches and casings

Medical & Laboratory
– Petri dishes and test tubes
– Diagnostic trays and pipette racks

Construction
– Foam insulation boards (EPS)
– Lightweight filler materials

Advantages of PS
– Excellent clarity and gloss (GPPS)
– Good dimensional stability and rigidity
– Lightweight and low cost
– Easy to mold and color
– Printable and suitable for vacuum forming
– Low dielectric constant (suitable for electronics)

Injection Molding Guidelines for PS

1. Drying Requirements
PS is generally non-hygroscopic and does not require drying under normal conditions.
– Drying only if stored in humid conditions: 80 °C for 2–3 hours

2. Melt and Mold Temperatures
– Melt temperature: 180–280 °C (limit to 250 °C for flame-retardant grades)
– Mold temperature: 40–50 °C for standard parts

3. Injection Pressure & Speed
– Pressure: 200–600 bar (lower than for most engineering plastics)
– Speed: High-speed injection preferred to ensure good fill and surface quality

4. Runner and Gate Design
– Use wide gates for better fill and reduced stress
– Typical gate diameter: 1.0–1.5 mm
– Hot runners are possible but require careful temperature control

Common Molding Issues
– Brittleness: Use HIPS for better impact resistance
– Voids or bubbles: May result from fast injection or air entrapment
– Flow marks: Optimize gate size and injection speed
– Warpage: Use uniform wall thickness and mold temperature control

Final Thoughts
Polystyrene is a staple in manufacturing for low-load, high-volume products where appearance, cost, and ease of processing are key. With proper handling, it provides reliable results in everything from electronics enclosures to everyday disposable items.
If you’re working with PS and need help optimizing molding parameters or selecting between GPPS, HIPS, or EPS, our materials team can provide expert guidance.