ASA, and it is not close. It carries the only excellent UV rating in this site's material data; PA12, PCTG and PEEK share the next tier down at good.
ASA is chemically ABS's neighbour with an acrylic component replacing the butadiene that UV attacks. Everything else — 240 to 265 °C nozzle, 95 to 110 °C bed, 0.4 to 0.8% contraction, an enclosure requirement — is ABS behaviour, so if you can print one you can print the other.
How the others fail, specifically
They do not all fail the same way, and knowing which failure you are buying matters.
- PLA goes chalky and brittle within a season, and separately sags at 52 to 60 °C — a dark part in direct sun reaches that easily. Two independent disqualifications.
- ABS yellows and cracks as UV degrades the butadiene phase. Mechanically fine, cosmetically ruined, then structurally ruined.
- PETG is rated good and is a reasonable second choice. It survives UV far better than PLA and holds 68 to 80 °C, but it creeps under sustained load in heat.
- Nylon absorbs water from the air, and outdoors that never stops. Dimensions move and stiffness drops.
The failure nobody plans for
Water in the layer lines. An outdoor part is porous along its layer interfaces, and water gets in, then freezes, then expands.
Freeze-thaw cycling splits parts that the UV would never have touched. The defence is more walls and higher extrusion temperature — a denser, better-bonded part — rather than a different polymer.
Practical outdoor design
- Four or more perimeters, and no sparse infill exposed at a cut face
- Print hot, for layer adhesion, since that is where water enters
- Avoid flat upward-facing surfaces where water can pool
- Design drainage into anything that can hold a puddle
The cheap alternative
Paint. A UV-stable primer and topcoat protects a PETG or even a PLA part surprisingly well, and for a part that is going to be painted anyway the material question largely disappears.
Rank materials against your own outdoor requirements in the material selector, and see the full profile on the ASA page.