PMMA (Acrylic) vs Polystyrene (PS)
PMMA (acrylic) and polystyrene (PS) are both transparent, rigid, low-cost plastics, but they target different jobs. Acrylic offers far superior optical clarity, UV and weather resistance, and better scratch resistance, making it the choice for displays, lenses, and signage. Polystyrene is cheaper and easy to mold but brittle (elongation ~2%) and yellows outdoors. The trade-off is optical and weather quality versus raw cost.
The verdict
Choose PMMA/acrylic for optical clarity, UV and weather resistance, and scratch-resistant transparent parts like displays, lenses, and outdoor signage. Choose polystyrene for the lowest-cost rigid, clear, or opaque indoor parts where brittleness and poor weathering are acceptable.
Side-by-side data
| Property | PMMA (Acrylic) | Polystyrene (PS) |
|---|---|---|
| Category | Plastic | Plastic |
| Density (g/cm³) | 1.18 | 1.05 |
| Tensile strength (MPa) | 70 | 45 |
| Yield strength (MPa) | 65 | 45 |
| Elongation (%) | 5 | 2 |
| Hardness | M95 | M70 |
| Max service temp (°C) | 80 | 70 |
| Machinability | ●●●●● | ●●●●● |
| Corrosion resistance | ●●●●● | ●●●●● |
| Relative cost | ●●●●● | ●●●●● |
| Thermal cond. (W/m·K) | 0.19 | 0.14 |
| Typically used for | Clear, optical & display parts | Cheap rigid housings & packaging |
Which should you choose?
Choose PMMA/Acrylic when…
- Optical clarity is critical — acrylic has excellent light transmission for lenses and displays
- Outdoor UV and weather resistance matter; acrylic resists yellowing far better than PS
- Scratch resistance is needed for viewing surfaces and signage
- The part is a clear cover, light guide, or display window
- Higher impact tolerance than PS is helpful (acrylic elongation ~5% vs PS ~2%)
- Service temperature near 80 C is acceptable (slightly above PS ~70 C)
Choose Polystyrene (PS) when…
- Lowest cost is the priority — PS (~1.0) undercuts acrylic (~1.5)
- The part is a cheap rigid housing, packaging, or disposable item
- It is used indoors, away from UV that would yellow and embrittle it
- Easy injection molding of high volumes is needed
- Optical and weather performance are not requirements
- Brittleness (elongation ~2%) is acceptable for the application
Key differences that matter
- Acrylic far outperforms PS in optical clarity, UV resistance, and weatherability — the core reason to choose it
- PS is cheaper (~1.0 vs ~1.5) and easy to mold, suiting disposable and low-cost rigid parts
- Both are brittle, but PS is more so (elongation ~2% vs acrylic ~5%)
- Acrylic resists scratching and yellowing; PS scratches easily and yellows outdoors
- Acrylic tolerates a slightly higher service temperature (~80 C vs PS ~70 C)
- Acrylic has higher tensile strength (~70 vs ~45 MPa)
- Neither is impact-tough — for transparent impact resistance, polycarbonate is the upgrade
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Open the Material SelectorGet a Quote →Frequently asked questions
Why is acrylic better for outdoor use than polystyrene?
Acrylic has excellent inherent UV and weather resistance — it stays clear and does not yellow or embrittle over years of sun exposure, which is why it dominates outdoor signage and glazing. Polystyrene degrades quickly under UV, yellowing and becoming even more brittle. For any weather-exposed transparent part, acrylic is the clear choice.
Are both brittle?
Yes, both are relatively brittle with low elongation, but polystyrene is worse (about 2% elongation versus acrylic's 5%). Neither absorbs much impact before cracking. If you need a transparent material that resists impact, polycarbonate (with ~110% elongation) is the appropriate step up from either acrylic or PS.
Which has better optical clarity?
Acrylic. It offers superior light transmission and optical quality, making it ideal for lenses, light guides, displays, and museum glazing. Polystyrene can be made clear and is used for cheap transparent packaging, but its clarity, scratch resistance, and yellowing behavior are inferior. For optical-grade transparency, acrylic is the standard.
When does the cost difference justify polystyrene?
When the part is a high-volume, indoor, non-optical item — disposable cups, cheap rigid housings, packaging, or toys — PS's lower cost (~1.0 vs ~1.5) and easy molding win. As soon as clarity, scratch resistance, or outdoor durability matter, acrylic's performance justifies its modest premium.
Property values are typical/nominal figures for early-stage guidance only and vary by temper, grade, supplier and heat treatment. Confirm critical specifications against a certified datasheet or with an mfgiq engineer before production.