Polycarbonate is the go-to when you need impact strength that ABS can’t touch. But put it outside, and the story gets complicated.
I’ve seen designers spec polycarbonate for outdoor enclosures because it’s “tough” and “UV-stabilized” — only to have those same parts yellow in eighteen months and crack by year three. Here’s the thing: standard PC does not like the sun. Its molecular backbone absorbs UV radiation, and that absorption drives chain scission, yellowing, and embrittlement. The rate depends entirely on whether you’ve paid for protection.
Let’s look at what accelerated weathering data says about how long PC actually lasts — and when you’d be better off with ASA instead.
What UV Does to Standard PC
PC absorbs strongly in the UV spectrum — that’s why it yellows faster than many other engineering plastics. The photodegradation mechanism is a photo-Fries rearrangement followed by photo-oxidation. Layman’s terms: the UV photons break the carbonate bonds, producing colored byproducts that turn the material yellow, then amber, then brittle.
Standard (un-stabilized) PC starts showing visible color change at around 200-300 hours of QUV exposure — a ΔE of 3-5. At 1000 hours, you’re looking at ΔE 6-8 and noticeable loss of ductility. By 2000 hours, impact retention drops to roughly 40% of original. The material that started as a 15 ft-lb/in notched Izod part now behaves more like a brittle styrene.
Outdoor life for standard PC: 1-3 years in most climates. Less in high-UV regions like Arizona or the Australian outback.
UV Stabilization: What Works and What Doesn’t
“UV-stabilized PC” is not a single thing. The performance depends on the stabilizer package, and there are three main approaches:
UV absorbers (UVA) work like sunscreen — they absorb UV radiation and dissipate it as heat before it reaches the polymer backbone. Benzotriazoles and triazines are the most common. Effective, but they have a finite capacity. Once consumed, degradation accelerates.
HALS (hindered amine light stabilizers) scavenge free radicals generated during photo-oxidation. They don’t absorb UV directly — they interrupt the chain reaction that follows. HALS are regenerative, meaning they can cycle through multiple stabilization events. They’re the gold standard for polyolefins and work well in PC too.
Carbon black is the oldest, cheapest, and most effective UV stabilizer ever discovered. It absorbs across the entire UV-visible spectrum and acts as a radical scavenger. The catch: you get black parts. If your customer wants white, gray, or any color that isn’t black, carbon black isn’t an option.
Premium UV-stabilized PC combines HALS with a UV absorber for synergistic protection. That’s the package that pushes outdoor life to 5-7 years.
QUV Data: PC vs. ASA Head-to-Head
ASA is PC’s main competitor for outdoor applications. Same acrylonitrile-styrene backbone as ABS, but with an acrylate rubber that does not absorb UV. The result: dramatically better weatherability without the cost of premium stabilizer packages.
| Property | PC (Std) | PC (UV-Stab) | ASA |
|---|---|---|---|
| UV Stabilizer Type | None | HALS + UV | Built-in |
| ΔE @ 2000h QUV | 8-12 | 2-4 | <2 |
| Impact Retention @ 2000h | 40% | 80% | 90% |
| Outdoor Life | 1-3 years | 5-7 years | 5-10 years |
| Cost Premium vs Std PC | — | +20-30% | +25-40% |
The table tells a clear story. Standard PC is cheap upfront but degrades fast. UV-stabilized PC closes the gap significantly — ΔE drops from 8-12 to 2-4, impact retention doubles, and outdoor life triples. But ASA matches or beats UV-stabilized PC on every weatherability metric. ΔE under 2 at 2000 hours. 90% impact retention. 5-10 year outdoor life.
The material cost premium for ASA vs. UV-stabilized PC is comparable — 25-40% over standard PC vs. 20-30%. But ASA processes at lower temperatures (420-460°F melt vs. PC’s 500-600°F), which means faster cycles and less energy per shot.
When PC Still Wins
ASA beats PC on weatherability, but PC beats ASA on raw mechanical performance. UV-stabilized PC delivers notched Izod impact of 12-16 ft-lb/in — ASA sits at 4-8 ft-lb/in. If your part needs to survive hail, impact, or abuse while living outdoors, PC is the right answer.
Specific applications where PC makes sense:
Outdoor equipment housings that take physical abuse — pressure washers, groundskeeping equipment, construction tools. The impact strength advantage justifies the stabilizer cost.
Transparent or translucent outdoor parts. PC is inherently transparent. ASA is opaque. If your design requires light transmission — skylights, solar panel covers, outdoor lighting lenses — PC is the only option. Use a UV-stabilized grade with a co-extruded UV-protective cap layer for maximum life.
High-temperature outdoor environments. PC has an HDT of 260-280°F at 264 psi. ASA is around 200-220°F. In applications where the part sees both sun exposure and heat buildup — dark-colored enclosures in direct sunlight — PC maintains its structural integrity better.
When to Switch to ASA
For most non-structural outdoor enclosures, ASA is the smarter call over UV-stabilized PC. You get comparable weatherability, lower processing costs, and better color stability over time.
I’ve worked with a customer who switched from UV-stabilized PC to ASA for an outdoor telecom enclosure. The PC parts were yellowing after 3 years in the field — not failing structurally, but the customer rejected the appearance. ASA parts from the same tool, same cycle time, 4 years in and the color is still within spec. The material cost was slightly higher, but the elimination of field replacement costs made it a net win.
Good candidates for ASA:
- Outdoor enclosures that don’t carry high mechanical loads
- Automotive exterior trim and mirror housings
- Marine and RV components
- Signage and architectural elements
- Garden equipment and outdoor power tool housings
For parts that need both outdoor durability and structural strength — consider a PC/ASA blend. You get PC’s impact strength with improved weatherability at a cost somewhere between the two.
The Five-Year Reality
Pull a non-stabilized PC part off an outdoor installation after 5 years and you’ll likely see yellowing, surface micro-cracks, and a 50-60% loss of impact strength. A UV-stabilized PC part from the same environment will show measurable color shift (ΔE 3-5) but retain 70-80% of its original impact. An ASA part will look and perform nearly as it did on day one.
The choice comes down to your part’s requirements. Impact strength or appearance? Clear or opaque? What temperature does it see? Answer those questions, and the material selection becomes straightforward.
Need help selecting the right material for your outdoor injection-molded part?
We run UV-stabilized PC, ASA, PC/ASA blends, and dozens of other outdoor-rated materials daily. Contact our engineering team with your part design and environment — we’ll give you a data-backed recommendation.