PETG is great — but put it in the sun and it'll yellow and crack in months. ASA was built for outdoors. Here's the complete comparison for 2026.
Direct sun exposure: Always choose ASA. UV stabilizers built in, lasts 5-10+ years outdoors without yellowing or cracking.
Shaded/wet outdoor only: PETG is fine. No UV degradation risk, cheaper and easier to print.
Hot environments (60°C+): PETG may warp or soften. Use ASA (HDT 95-100°C vs PETG's 70-80°C).
PETG is one of the most popular 3D printing filaments — and for indoor use, it deserves every bit of its reputation. Strong, flexible enough to absorb impact, moisture-resistant, easy to print. But expose it to direct sunlight, and the physics work against it.
PETG (Polyethylene Terephthalate Glycol) does not have UV stabilizers in its standard formulation. The ultraviolet component of sunlight — specifically UVA (315-400nm) — breaks down polymer chains through a process called photodegradation. Over months, this causes yellowing of clear/light colors, surface crazing (micro-cracks), embrittlement, and eventually structural failure.
ASA (Acrylonitrile Styrene Acrylate) was specifically engineered to solve this problem. The acrylate rubber phase in ASA absorbs and dissipates UV energy without degrading the polymer backbone. This is the same reason ASA is used in automotive trim, outdoor signage, and garden furniture.
• Yellowing (especially clear/white/light colors)
• Surface becomes chalky, loses gloss
• Micro-cracks appear on stressed surfaces
• Impact resistance reduced 30-50%
• Clear PETG becomes opaque
• Color remains stable
• Surface gloss largely preserved
• No significant cracking or crazing
• Mechanical properties essentially unchanged
• Ready for another 4-9 years outdoors
| Property | ASA | PETG | Winner |
|---|---|---|---|
| UV Resistance | ★★★★★ Excellent | ★★☆☆☆ Poor | ASA |
| Weathering (Rain/Humidity) | ★★★★☆ Very Good | ★★★★☆ Very Good | Tie |
| Heat Deflection Temp | 95–100°C | 70–80°C | ASA |
| Impact Resistance | ★★★★☆ Good | ★★★★☆ Good | Tie |
| Print Difficulty | ★★★☆☆ Moderate | ★★☆☆☆ Easy | PETG |
| Warping Risk | High (needs enclosure) | Low | PETG |
| Fumes | Significant (ventilate) | Low | PETG |
| Long-term Outdoor Life | 5–10+ years | 6–18 months (sun) | ASA |
| Cost (1kg spool) | $18–30 | $15–22 | PETG |
| Color Stability | Excellent — no yellowing | Yellows in UV | ASA |
| Layer Adhesion | Very Good | Excellent | PETG |
| Available Colors | Good selection | Very wide selection | PETG |
Summary: ASA wins on outdoor performance metrics; PETG wins on printability and cost.
Use-case recommendations for common outdoor applications:
Direct sun exposure year-round degrades PETG in 1-2 seasons
UV + heat resistance required; ASA handles both
High heat + UV; PETG softens at 60-70°C common on car surfaces
Both resist water; PETG is easier to print if UV is not a factor
Shade = minimal UV. PETG is fine. ASA if mixed sun/shade.
Sun + flexing + heat impact; ASA's UV stability protects long-term
Always sun-exposed; PETG fades and cracks within 1-2 years
Short duration means UV degradation is not a concern
ASA's biggest downside is warping. Like ABS, it shrinks significantly as it cools, pulling corners off the bed and causing layer delamination on large prints. If you've never printed ABS, ASA will require a learning curve.
Without an enclosure, ASA is very difficult to print at any useful size. Options:
Polymaker PolyLite ASA
Consistent, low warping for ASA, good UV performance. ~$22/kg. Best all-around.
eSUN ASA
Budget-friendly (~$18/kg), decent quality. Warps more than Polymaker. Good for first-time ASA users.
Prusament ASA
Premium quality, tight tolerances (~$28/kg). Best choice for critical outdoor parts.
Polymaker PolyLite PETG
Reliable, low stringing, consistent diameter. ~$18/kg. Best default choice.
Bambu Lab PETG Basic
Excellent for Bambu printers, dialed-in profiles. ~$20/kg. Consistent quality.
Sunlu PETG
Best budget option (~$15/kg). Slightly more stringing but very affordable for outdoor experiments.
Q: Can I UV-coat PETG to make it last longer outdoors?
Yes, applying a UV-resistant clear coat (like Rust-Oleum Crystal Clear or automotive UV-clear lacquer) can significantly extend PETG's outdoor life — from 6-18 months to potentially 3-5 years. It's extra work and the coating can chip over time, but it's a viable option if you're already comfortable printing PETG. Sand lightly first (400 grit) for better adhesion.
Q: Is PETG UV resistant at all?
PETG has very minimal natural UV resistance compared to UV-stabilized materials. Some manufacturers add UV stabilizers, so check the datasheet — but most standard PETG is not UV-stable. ASA, polycarbonate, and UV-stabilized PETG variants are better choices for long-term sun exposure.
Q: What about polycarbonate (PC) for outdoor use?
PC has excellent impact resistance and decent heat resistance, but its UV resistance is actually poor without coatings — it yellows faster than PETG in many cases. ASA remains the go-to choice for outdoor UV resistance among common FDM materials. See our Polycarbonate guide for full details.
Q: Does ASA smell bad when printing?
Yes. ASA produces styrene fumes during printing, similar to ABS but slightly less intense. Always print in a well-ventilated area, use an enclosure with a carbon filter if possible, and avoid breathing the fumes. Some people are more sensitive than others. PETG is much more pleasant to print with in terms of fumes.
For anything that will see direct sunlight, ASA is the clear winner — no debate. The UV degradation of PETG is not hypothetical; it's measurable and consistent across testing. If your part is outside in the sun for more than one summer, use ASA.
For shaded outdoor applications or temporary outdoor use (under 6 months), PETG is perfectly acceptable and much easier to print. If you don't have an enclosure, PETG is also the pragmatic choice — ASA without an enclosure is a recipe for failed prints.
The best workflow: buy a spool of ASA, build or buy an enclosure, and learn to print it. Once you can print ASA reliably, you'll have access to the best outdoor FDM material available without exotic printers or materials.
ASA Filament Complete Guide
Full settings, tips and brands
PETG Filament Complete Guide
Everything about PETG printing
ABS vs ASA Comparison
The other outdoor comparison
PETG vs PLA Guide
The most common filament choice
Polycarbonate (PC) Guide
High-performance alternative
Best Filament for Functional Parts
Strength and durability focus