The short answer
General-purpose (crystal) polystyrene is clear, stiff and brittle. North American grades run about 1.5–23 g/10 min melt flow at 200°C / 5 kg, 1.04–1.05 g/cm³ density and 94–108°C / 201–227°F Vicat softening. Low-flow, heat-resistant grades go into foam and oriented sheet. Easy-flow grades fill thin-wall cups and cutlery, and many contain mineral oil, which lowers heat resistance. Match melt flow, Vicat and oil content together.
Have a part number or drawing callout?
Paste it as written. A polymer chemist will tell you which grade it calls for, suggest equivalents and quote it by email.
This page covers general-purpose, or crystal, polystyrene (GPPS). The name refers to its clarity; the polymer is amorphous. For the rubber-modified, opaque version see GPPS vs. HIPS. Typical values for both are on polystyrene properties, and grades by product are on the polystyrene page. Molded foam such as coolers and protective packaging is made from expandable PS beads (EPS), a separate product from GPPS pellets.
Typical spec window
| Property | Typical range | Test method |
|---|---|---|
| Melt flow | About 1.5–23 g/10 min; heat-resistant grades about 1.5–4, easy-flow grades about 10–23 | ASTM D1238 or ISO 1133, 200°C / 392°F, 5 kg |
| Density | 1.04–1.05 g/cm³ / 0.0376–0.0379 lb/in³ | ASTM D792 or ISO 1183 |
| Vicat softening | 94–108°C / 201–227°F | ASTM D1525 (load and rate as stated on each sheet) |
| Heat deflection, 1.8 MPa | About 77–90°C / 171–194°F unannealed; annealed bars read higher | ASTM D648 |
| Tensile strength | 28–53 MPa / 4,000–7,700 psi; lowest in the highest-flow grades | ASTM D638 |
| Flexural modulus | About 3.0–3.4 GPa / 430,000–490,000 psi | ASTM D790 |
| Elongation at break | 2–3% | ASTM D638 |
| Notched Izod | About 16–21 J/m / 0.3–0.4 ft·lb/in | ASTM D256 |
| Light transmission | 88–90%, refractive index 1.59, where listed | ASTM D1003; ASTM D542 |
Typical ranges from 2026 North American data sheets from AmSty and TotalEnergies. Your grade's own data sheet and the lot COA are what count.
What it’s used for
- Clear drink cups, tumblers and cutlery
- CD and DVD jewel boxes and other clear cases
- Medical and lab ware such as dishes and trays
- Foam food trays, egg cartons and clamshells (extruded foam sheet)
- Oriented PS (OPS) sheet for clear thermoformed packaging
- Extruded foam insulation board (XPS), housewares and display parts
How to tell grades apart
- Heat-resistant (low flow). Melt flow about 1.5–4 and Vicat about 105–108°C / 221–227°F. Used for foam sheet, OPS sheet and medical parts. Examples: AmSty Styron 685D and TotalEnergies 595T.
- General purpose (medium flow). Melt flow about 5–10, for jewel boxes, housewares and general clear parts. Examples: Styron 668 (5.6), Styron 666D (8.0) and TotalEnergies 525B (9.0).
- Easy flow (high flow). Melt flow about 13–18, for thin-wall cups and cutlery with long flow paths. Many contain white mineral oil, listed on the safety data sheet, which raises flow and drops Vicat to about 94–99°C / 201–211°F. Examples: Styron MC3700 (18) and TotalEnergies 500B (14).
- Oil-free high flow. Heat and flow are not a fixed trade-off. AmSty Styron 611 and TotalEnergies 523W run about 11 g/10 min with Vicat near 106–108°C / 222–226°F, and TotalEnergies 503 reaches 23 g/10 min at 106°C / 222°F. TotalEnergies lists these high-heat, high-flow grades for foam board, loose fill and masterbatch carrier use. Check the safety data sheet for mineral oil when heat matters.
- Clarity and purity. All GPPS is clear, so specks, gels and yellowness show. Additive-free grades such as Styron 665 are offered for film and other sensitive uses.
- Not GPPS. HIPS adds rubber for impact and is opaque. EPS molded foam is made from expandable beads sold by bead size and pentane content, not by melt flow.
What to put on your RFQ or PO
- Melt flow with the condition. 200°C / 392°F and 5 kg, nominal value and range.
- Heat. The Vicat (with its load and rate) or heat deflection your part or process needs.
- Process. Injection molding, foam sheet, OPS sheet, XPS board or extrusion.
- Mineral oil and additives. Whether your process or customer limits mineral oil, lubricants or zinc stearate, or needs an additive-free grade.
- Food contact. The producer's FDA letter (21 CFR 177.1640) for the exact grade.
- Color. Natural clear or tinted, and whether you add color concentrate at the press.
- COA values to check. Melt flow on each lot, and color or yellowness for clear parts if the producer reports it.
- Packaging. Gaylords or 25 kg (55 lb) bags. GPPS takes up almost no water, but cold pellets opened in a warm plant can pick up condensation, so keep packages sealed until they warm up.
- Quantity and release size. Total quantity, how much per release and how often.
A polymer chemist reviews every request and checks the grade against your process before we quote. Every prime lot from our suppliers ships with a COA, and orders start at one gaylord.
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- Same melt flow condition, Vicat and oil content from another producer. The closest swap. Check clarity, color and cycle time on first articles.
- HIPS or a GPPS/HIPS blend. When parts crack in use and clarity is not needed. See GPPS vs. HIPS.
- Clarified PP random copolymer. Tougher and more chemical resistant, but hazier and less stiff. See clear PP random copolymer.
- SAN. Clear and stiff with better chemical resistance than GPPS. See ASA and SAN.
- Polycarbonate or acrylic. For clear parts that must take impact or heat. See PC vs. acrylic and best plastic for clear parts.
Common processing problems
- Parts crack at ejection or in use: brittle cracking parts
- Black specks that show in clear parts: black specks contamination
- Cracks from oils, fats or cleaners: environmental stress cracking
- Parts sticking in the mold: parts sticking in mold
- Splay from condensation on cold pellets: splay silver streaks
Common questions
What melt flow GPPS do I need?
Start from the grade that runs your mold now, measured at 200°C / 5 kg. Low-flow grades (about 1.5–4 g/10 min) suit foam and oriented sheet, medium-flow grades (about 5–10) general clear parts, and easy-flow grades (about 13–18) thin-wall cups and cutlery. Check Vicat too, since many easy-flow grades get their flow from mineral oil.
Is crystal polystyrene the same as GPPS?
Yes. Crystal refers to its glass-like clarity, not to crystallinity. GPPS is amorphous, which is why it is clear and shrinks a low, even 0.3–0.8%.
Does GPPS need to be dried?
Usually not, since polystyrene absorbs almost no water. Dry only regrind, resin stored in humid conditions or pellets with condensation, at about 71–75°C / 160–167°F for 1–2 hours.
Is GPPS used to make foam?
Yes, for extruded foam: foam sheet for trays and egg cartons and XPS insulation board are made from GPPS pellets with a blowing agent. Molded foam such as coolers and protective packaging uses expandable PS (EPS) beads, a separate product.
Tell us the grade you run now
A polymer chemist reviews every request, then matches your grade or finds a qualified equivalent and prices it.
What to send for an accurate quote
- The grade name, from any supplier, or a data sheet
- Color (natural, black or a custom match)
- Fill type and percentage, if any
- Melt flow, if you know it
- Quantity for this order and what you use in a year
- Ship-to city and state or province