PC vs Acrylic (PMMA) for Outdoor Clear Parts: UV, Impact, and Cost Compared

You need a clear plastic part that lives outdoors — a lighting cover, a camera housing, a solar component lens. Two materials dominate the conversation: polycarbonate and acrylic. And both will let you down if you pick the wrong one.

Here’s the thing: PMMA stays crystal-clear for over a decade outdoors but shatters if a stray tool hits it. UV-stabilized PC takes a beating but yellows noticeably in five to seven years. I’ve measured the color shift on both after 2,000 hours of QUV testing — the numbers tell a clear story. The real solution comes from combining them.

The Core Tradeoff: UV Stability vs. Impact

Outdoor clear parts face three enemies: UV radiation that breaks polymer chains, thermal cycling that drives microcracks, and physical impact from hail, debris, or maintenance. No single commodity transparent plastic handles all three well.

UV damage in transparent plastics isn’t just cosmetic. When PC yellows, it shifts the color temperature of transmitted light. A lighting cover that starts at 4,000K color temperature can drift to 3,200K over five years — that warm amber glow isn’t a design choice, it’s polymer degradation. The loss in light output compounds: a 5% transmission drop means 5% more fixtures to meet the same illuminance spec.

Impact in transparent parts is a safety problem, not just a breakage problem. A shattered lighting cover over a parking lot or a cracked camera housing protecting optics creates real liability. Glass avoids the yellowing but creates the same fall-and-shatter risk.

PMMA (Acrylic): Ten-Year Clarity, One-Hit Fragility

PMMA is the baseline for outdoor optical clarity. Light transmission hits 92% — higher than any transparent engineering plastic. The UV resistance is outstanding because the polymer backbone simply doesn’t absorb UV wavelengths the way PC’s aromatic structure does. A QUV test at 2,000 hours shows ΔE color change under 1 — essentially invisible to the human eye.

The brittleness problem. Notched Izod impact for PMMA sits around 20 J/m. That is low. For comparison, standard polycarbonate runs 600–900 J/m. A PMMA lighting cover that survives ten years of Arizona sun can still crack from a single branch strike during windstorm maintenance. I’ve seen 6 mm thick PMMA skylights fail from the thermal stress of a hot day followed by a sudden hailstorm.

Scratch resistance is PMMA’s other advantage. Pencil hardness of 2H–3H means it survives cleaning, dust abrasion, and handling better than PC (HB). But that hardness doesn’t help against impact — it makes the material more notch-sensitive.

UV-Stabilized PC: Tough Until It’s Not

Polycarbonate with UV stabilizers is the impact champion. Notched Izod of 600–900 J/m is roughly 250× what PMMA delivers. Drop a PC cover from six feet onto concrete — it bounces. The stabilizer package helps extend outdoor life, but it doesn’t solve the fundamental problem: PC’s aromatic backbone absorbs UV and degrades.

The yellowing timeline is real. UV-stabilized PC shows ΔE of 3–5 after 2,000 hours of QUV. In real-world outdoor exposure, that translates to visible yellowing in years five through seven. The stabilizer additives delay the onset, but once they’re consumed, degradation accelerates. I tested a PC dome light cover that looked fine at year four and was visibly amber at year six.

The hidden cost of stabilizers. UV additives increase the material cost by 10–15% over standard PC. They also affect processing — the additive package can plate out on mold surfaces over long production runs, requiring periodic purging. And the UV protection is limited to what the additive loading provides. Double the stabilizer concentration doesn’t double the outdoor life. There’s a diminishing return curve, and most commercial UV-stabilized grades live on the flat part.

Transmission is lower too. PC transmits about 88% of visible light vs PMMA’s 92%. That 4% difference matters in applications where every lumen counts — solar concentrators, optical sensors, LED light guides.

PC/PMMA Co-extrusion: The Best of Both

Here’s where the data gets useful. You can cap a UV-stable PMMA layer over a PC substrate in a single co-extrusion process. The PC core provides the impact strength. The PMMA cap provides the UV protection and surface hardness. Together, they outlast either material alone.

What the co-ex gives you. Light transmission reaches about 90% — a compromise, but closer to PMMA than PC. Notched Izod drops slightly from pure PC to about 600 J/m because the PMMA cap is thin and the PC core still dominates impact behavior. The PMMA layer takes the UV hit, so ΔE stays under 1 after 2,000 hours — same as pure PMMA. Outdoor life extends to 10+ years because the UV never reaches the PC substrate.

The cap thickness matters. A 0.3–0.5 mm PMMA cap is typically enough for outdoor service. Below 0.3 mm, pinholes or thickness variation can expose the PC to UV. Above 0.5 mm, you’re spending money on PMMA that isn’t contributing proportionally. I spec 0.4 mm cap thickness as default and adjust up only if the part sees extreme UV exposure or frequent abrasive cleaning.

Processing complexity. Co-extrusion requires a two-material feed system and precise temperature control across the interface. Not every injection molder runs it. The tooling cost is higher because flow channels for both materials must be balanced. And if the melt temperatures aren’t matched within 10–15°C, the bond interface weakens and delamination becomes a risk.

Direct Comparison

When to Pick Which

Choose PMMA when: the part doesn’t see impact threat — interior lens covers, nameplates, display windows in controlled environments. The optical clarity and UV stability are unmatched. Just design for the brittleness: thicker walls, generous radii, no sharp notches.

Choose UV-stabilized PC when: impact is the primary concern and the part has limited outdoor life or a known replacement cycle. LED troffer lens covers that get replaced when the fixture is serviced? PC with stabilizers works fine. A permanently installed skylight that sits in direct sun for twenty years? PC will disappoint you.

Choose PC/PMMA co-ex when: you need optical clarity AND impact resistance AND ten-year outdoor life. This is the solution for solar panel covers, outdoor camera housings, security lighting globes, and any part where replacement cost exceeds the material premium. The 1.5× cost multiplier is real, but compare that against replacing a yellowed or shattered part every five to seven years. The numbers usually favor co-ex on lifecycle cost.

I’ve run the QUV data and impact testing on all three options across dozens of projects. If your part needs to stay clear, stay intact, and stay outdoors, send us the requirements — we’ll help you pick the right construction before steel hits the press.