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Resin Data
GPPS

Poliestireno de Uso General

GPPS·Polystyrenes·Amorphous

GPPS (General Purpose Polystyrene) is the "crystal" grade of polystyrene — the most transparent, glossy and rigid of the entire PS family. When people talk about "crystal PS" or simply "transparent PS" they're talking about GPPS: the same polymer as PS but without the butadiene elastomer phase that HIPS has, which gives it 90–92% optical clarity (more than glass in thin sections) and a factory-fresh gloss that requires no polishing.

You know it by brands like Styron (Trinseo, the original), Polystyrol (BASF), Styrolux (INEOS Styrolution), SABIC PS. It's the material par excellence for CD/DVD jewel cases, disposable transparent cups, cosmetic packaging, electronics blisters, commercial displays, scale modeling (Tamiya, Revell), food clamshell trays. Its Achilles heel: extreme brittleness (breaks like glass, no warning). Here we have compiled the reference ranges from the PDS, plus the questions that come up over and over on the shop floor: GPPS vs PS vs HIPS, MFI grades, food-safe, unbeatable costs vs PMMA.

Share your experience in the comments — ranges vary by manufacturer and MFI, and collective discussion is what gets us out of trouble on the floor.

The ranges shown in these data tables were compiled by the MVPS team from various parameter sheets and literature, integrating the lower and upper limits for each material type.

This information must be carefully reviewed when developing injection molding processes. Final ranges and processing tolerances are the responsibility of the engineer in charge.

These ranges are not recommended for developing specific process tolerances. MVPS always recommends requesting and consulting the supplier's data sheet.

General Properties

Chemical StructureAmorphous
Specific Gravity (Density)1.05:1
L/D Ratio17 – 24
Compression Ratio1.5 – 4
Tonnage Factor3.09 – 6.18kN/cm²
Thermal Diffusivity0.1319mm²/s
Max Shear Rate40,0001/s
Shrinkage0.4 – 0.7%
Regrind25%
Heat Deflection (HDT) @ 1.82 MPa80°C
Glass Transition (Tg) @ 10°C/min100°C
Vicat Softening @ 50N94°C

Drying

Drying Temperature60 – 71°C
Drying Time1 – 3h
Recommended Moisture0.02%
Recommended Dryer TypeAir
Dew Point-40°C

Temperatures

Melt191 – 221°C
Nozzle191 – 221°C
Front191 – 210°C
Middle179 – 199°C
Rear171 – 191°C
Demolding54 – 82°C
Mold (Cooling)38 – 71°C
Feed Throat35 – 79°C

Processing

Back Pressure2.1 – 11.7bar
Screw Speed30 – 60RPM
Injection SpeedMedium – High
Barrel Occupancy25 – 75%
Injection Pressure400 – 1,000Pbar
Holding Pressure100 – 800Pbar
Cushion6.4 – 12.7mm

Mold

Runner Diameter3.05 – 6.1mm
Gate Diameter0.76 – 1.52mm
Gate Area0.46 – 1.82mm²
Wall Thickness0.99 – 3.99mm

Venting

Depth (Vent Depth)0.0203 – 0.0406mm
Land (Vent Land)0.508 – 1.02mm
Width (Vent / Clearance)3.05 – 6.1mm
Relief (Relief Channel)0.254 – 0.381mm

Frequently asked questions

Spoiler: they are the same. The name GPPS (General Purpose PolyStyrene) is technically a subset of PS — the crystal grade without rubber. In industrial practice, when someone says PS without qualification, they almost always mean GPPS. The name HIPS (High Impact PS) is used for the polybutadiene-modified grade (opaque, tough). Summary: GPPS = crystal PS = pure transparent PS. Density 1.04–1.05 g/cm³, 90–92% transparency, no elastomer, brittle.
GPPS: pure polymerized styrene, transparent, rigid, glossy, brittle (breaks on impact). HIPS: GPPS + 5–10% dispersed polybutadiene particles that absorb impact energy. Result: HIPS is matte opaque, 5–10× tougher than GPPS, but lower gloss and slightly lower rigidity. Rule of thumb: you need clarity → GPPS. You need impact resistance + opaque finish → HIPS. For transparent cold beverage cups, CD cases, modeling: GPPS. For opaque disposable cups, cheap toys, refrigerators: HIPS.
Low MFI (1–5 g/10min): high molecular weight, grade for sheet extrusion (blister thermoforming), better mechanical resistance. Medium MFI (8–15): grade for thick-part injection, balance of processability/properties. High MFI (16–34): low molecular weight, grade for thin-wall injection (disposable cups, commercial blisters), fills complex molds fast but more brittle. For optics: medium MFI (10–12). For disposable cups and high-volume production: high MFI (18–25). Common brands: Styron 615 NW (Trinseo, MFI 8), Styrolux 656C (INEOS), BASF Polystyrol 158K.
Yes, food-safe approved by FDA and EFSA for food contact in normal use. It has the same chemistry as general PS, so the same considerations apply: micro-migration of residual monomer to foods, higher with heat and fats. For cold disposable use (cups, product blisters) it is safe and widely used. For repeated hot or fatty foods, food-grade PP is preferable. The FDA limit is 0.1 mg/L in water — commercial products are 10,000× below.
Typical GPPS cost: 30–50% of PMMA, for three reasons: (1) raw material — styrene is one of the cheapest monomers in the world, produced at massive scale ($1000–1200/ton vs $1800–2500/ton for MMA), (2) production scale — global GPPS capacity ~10 million ton/year vs ~3 million ton/year for PMMA, (3) easier processing — melts at 180°C vs 230°C for PMMA, no mandatory drying, faster cycle = lower manufacturing cost. For disposable transparent parts or where premium optical look doesn't matter, GPPS is unbeatable in clarity/price ratio.
Normally no. GPPS is practically non-hygroscopic (<0.05% moisture at equilibrium). That's why the PDS marks 'Air' or no drying. Exceptions: (1) very high-quality optical parts (Fresnel lenses, optical CD masters) — light drying at 80°C × 2 h helps remove surface microhumidity and give crystalline clarity, (2) tropical climates (sustained RH >70%), (3) regrind exposed to humid shop floor. For disposable cup or blister production: straight to hopper, no drying.
The PDS marks 38–71°C, cold compared to other resins. Hot (55–65°C) = better gloss, better mold detail reproduction, lower residual stress (important to avoid later crazing with chemicals), but longer cycle. Cold (10–30°C, yes, as low as 10°C for thin walls) = ultra-short cycle, ideal for mass production runs of disposable cups and high-volume blisters. For cosmetic or optical transparent parts: 50–60°C. For disposable parts: 20–35°C to maximize throughput.
GPPS wins on: cost (30–50% cheaper), processing ease (lower temperature, flows better, no drying), faster cycle. PMMA wins on: optical clarity (92% vs 90% but more stable), UV resistance (PMMA doesn't yellow, GPPS yellows in 6–12 months in the sun), much better scratch resistance, better chemical resistance, biocompatible (PMMA is medical, GPPS is not), much better impact resistance (PMMA is brittle but less than GPPS). Rule: disposables, interior, low-cost packaging → GPPS. Premium, outdoor, optical, signage going outside → PMMA.
Interior signage: GPPS is perfect for illuminated letter signs, advertising displays, light boxes that don't go outdoors. Gloss and transparency at low cost. Do not use outdoors because it yellows in 6 months. Scale modeling: plastic modeling kits (Tamiya, Revell, Hasegawa) use GPPS with pigments integrated into the material — molded colors with fine detail that reproduces perfectly. Adhesion with modeling cement (essentially PS solvent) chemically welds the parts. It's been the basis of the scale modeling industry since the 1950s.
Technically yes (international recycling code #6), practically complicated in many countries. The key problem: clean rigid GPPS (CD cases, commercial blisters) is processable but municipal infrastructure rarely accepts it. For closed-loop internal recycling (in-plant regrind): the PDS marks 25% without significant loss. 2026 trend: brands like Styron CO2RE™ (Trinseo) are introducing grades with certified recycled content (PCR — Post Consumer Recycled), responding to European regulations and some US state regulations. For food-contact applications, PS PCR requires an FDA-approved process with functional barrier.

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