Clear plastics look interchangeable on the shelf, but acrylic and polycarbonate behave very differently once a part sees impact, heat, sunlight, machining or repeated handling. Acrylic (PMMA) is chosen for optical clarity, surface hardness and easy polishing. Polycarbonate (PC) is chosen when toughness and higher service temperatures matter more.
The short answer: choose acrylic when the part must look premium, transmit the most light and resist scratches, and it will not take hard impacts. Choose polycarbonate when the part must survive drops, impact or heat, or protect a person. On the manufacturers’ datasheets, acrylic transmits 92% of light against 88% for polycarbonate, while polycarbonate holds its shape up to 124 °C against 98 °C for acrylic.
What are acrylic and polycarbonate?
Acrylic, or PMMA, is a rigid transparent thermoplastic used for displays, light guides, diffusers, lenses and cosmetic covers. It is valued for its glass-like appearance and its natural resistance to weathering.
Polycarbonate is a transparent engineering thermoplastic built for tougher service: machine guards, safety windows, protective housings and rugged electronics covers, anywhere a clear part may take impact or vibration.
Both can be injection molded, CNC machined, thermoformed and fabricated from sheet. The differences show up in how each responds to stress, heat, scratching, sunlight and process conditions.
Acrylic vs. polycarbonate at a glance
| Property | Acrylic (PMMA) | Polycarbonate (PC) | What it means for your part |
|---|---|---|---|
| Light transmission | 92% | 88% to 89% | Acrylic is the clearer of the two |
| Refractive index | 1.49 | 1.58 | Matters for lenses and light guides |
| Heat deflection at 1.8 MPa | 98 °C | 124 °C | PC holds its shape at higher temperatures |
| Vicat softening point | 108 °C | 143 °C | PC softens later |
| Unnotched Charpy impact | Breaks at 20 kJ/m² | Does not break | PC is far tougher under impact |
| Surface hardness | Harder, more scratch resistant | Softer, may need a hard coat | Acrylic stays cosmetic longer when handled |
| Outdoor exposure | Naturally weather resistant | Needs UV-stabilized grades or coatings | Acrylic is simpler outdoors |
| Material cost | Usually lower | Usually higher | Acrylic is often the budget option |
Numbers are typical values for injection molding grades: PLEXIGLAS 8N for acrylic (Röhm) and Makrolon 2407 for polycarbonate (Covestro). They vary by grade and thickness, so confirm against the datasheet of the resin you specify.
Key differences that drive the choice
Optical clarity and appearance
Acrylic is usually the first choice when a premium clear look is the top priority. It transmits more light, shows low haze and polishes to an excellent edge, which suits displays, illuminated panels, lenses and customer-facing covers. Polycarbonate is also optically clear, but it is normally chosen for its mechanical performance; for industrial windows and protective covers its clarity is more than enough.
Impact resistance
This is where polycarbonate pulls ahead. In the same unnotched Charpy test, the acrylic grade breaks at about 20 kJ/m² while the polycarbonate grade does not break at all. That is why PC is the default for machine guards, safety shields and rugged electronics. Acrylic performs well in normal use, but it can crack under severe impact or concentrated stress.
Scratch resistance and surface care
Acrylic has the harder surface and resists scratches better. Polycarbonate is tougher but softer at the surface, so parts that are handled often and must stay cosmetic may need a protective hard coat.
Heat and outdoor exposure
Polycarbonate tolerates higher temperatures: its heat deflection temperature is about 26 °C higher and its softening point about 35 °C higher than acrylic’s. Outdoors the picture reverses: acrylic weathers very well on its own, while polycarbonate usually needs a UV-stabilized grade or coating for long-term sun exposure.
Molding clear parts: what changes with each resin
Clear parts show every flaw that an opaque part would hide: sink marks, flow lines, gate vestiges, weld lines, ejector marks and contamination. Both resins mold well, but they ask for different process windows.
| Setting | Acrylic (PLEXIGLAS 8N) | Polycarbonate (Makrolon 2407) |
|---|---|---|
| Drying before molding | 2 to 3 hours, at up to 98 °C | 2 to 3 hours at 120 °C, to 0.02% moisture or less |
| Melt temperature | 220 to 260 °C | 250 to 300 °C |
| Mold temperature | 60 to 90 °C | 80 to 120 °C |
Polycarbonate is the more demanding of the two: it needs a hotter process, and it must be dried to a very low moisture level or it degrades in the barrel, which shows up as splay and lost toughness. For optical surfaces with either resin, mold polish, gate location, venting and a stable process decide the result. A mold flow simulation helps place gates and weld lines away from the areas people look through.
Other ways to make clear parts
CNC machining
Useful for prototypes, low volumes and thick clear blocks. Acrylic machines and polishes especially well; polycarbonate needs controlled cutting parameters to avoid haze, burrs and cracking around features. See our CNC machining services.
Thermoforming and sheet fabrication
Large covers, shields and curved panels can often be made from sheet at a lower tooling cost than injection molding, with laser cutting, routing and bonding for flat or fabricated assemblies.
3D printing
Clear printed parts are useful for checking shape and fit, but they are not a production substitute for molded PMMA or PC: they usually need sanding or coating and behave differently mechanically and optically. See 3D printing services.
Where acrylic works best
- Displays, signage and point-of-sale fixtures.
- Lighting diffusers, light guides and lenses (see our work in lens technology).
- Cosmetic covers and electronics windows where appearance comes first.
- Machined prototypes that need polished edges and high clarity.
Where polycarbonate works best
- Machine guards and transparent safety barriers.
- Impact-resistant covers and protective windows.
- Rugged electronics windows and user-interface covers.
- Industrial housings that need visibility without giving up toughness.
How to choose between acrylic and polycarbonate
Start with the failure you need to prevent. If the part must stay crystal clear and polished in a low-impact environment, acrylic is usually the efficient choice. If it must survive abuse, run hot or protect an operator, polycarbonate deserves priority even if it costs more or needs a hard coat.
Design tips for clear plastic parts
- Keep wall thickness uniform to avoid sink and optical distortion.
- Use generous radii to reduce stress concentration and help the flow.
- Keep gates, ejector pins and witness marks out of the areas people look through.
- Define cosmetic and functional surfaces before tooling, and specify acceptable haze, scratches and visible defects in measurable terms.
- Check chemical exposure for polycarbonate: some cleaners, adhesives and solvents cause stress cracking.
- For outdoor parts, specify a UV-stabilized grade or coating, especially for polycarbonate.
Clear parts also make molding defects more visible, and tight tolerances on optical features add cost, so agree on both early.
What to include in a clear-part RFQ
- 3D CAD, preferably STEP.
- Target material, or the functional requirements if it is not chosen yet.
- Expected quantity and annual demand.
- Critical dimensions and tolerances.
- Cosmetic surfaces and optical quality expectations.
- Operating temperature, UV, impact and chemical exposure.
- Finish, texture, polish, coating and color requirements.
- Assembly details such as inserts, fasteners, adhesives or gaskets.
Common questions about acrylic and polycarbonate
Which is clearer, acrylic or polycarbonate?
Acrylic. Its molding grades transmit about 92% of light, against about 88% for polycarbonate, and it polishes to a better optical finish.
Which is stronger?
Polycarbonate is far tougher under impact: in the unnotched Charpy test it does not break, while acrylic breaks at about 20 kJ/m². Acrylic is stiffer and harder at the surface, but more brittle.
Which is better outdoors?
Acrylic weathers very well on its own. Polycarbonate can be used outdoors, but it usually needs a UV-stabilized grade or a protective coating for long-term sun exposure.
Can both be injection molded?
Yes. Polycarbonate needs a hotter process and very dry resin (0.02% moisture or less); acrylic molds at lower temperatures. Both need careful mold polish, gating and venting for optical surfaces.
Is polycarbonate always the better engineering material?
No. It is tougher, but acrylic is the better choice when clarity, scratch resistance, outdoor stability, easy polishing and cost matter more than impact performance.
Key takeaways
- Acrylic is the better visual material: clearer, harder and easier to polish.
- Polycarbonate is the better impact and heat material: it does not break where acrylic does, and it holds its shape about 26 °C hotter.
- Polycarbonate needs a hotter process and very dry resin to mold well.
- Choose by the failure you need to prevent, then confirm with the datasheet and a DFM review.
Not sure which clear plastic fits your part? Upload your CAD for a quote. Every quote includes a DFM review, and our engineers can help you choose between acrylic and polycarbonate for your clarity, impact and temperature needs. Learn more about our injection molding services.