Best filament for outdoor use: what survives sun and rain

Short answer

For anything that lives outside, ASA is the safe pick for full sun, PETG works for sheltered or mild exposure, and plain PLA is the one to avoid. The difference is ultraviolet light, which yellows and embrittles PLA within months while ASA is built to resist it.

How the weather breaks filament

Three forces age an outdoor print: ultraviolet light, heat, and moisture. UV is the killer for PLA. Sunlight turns it yellow and brittle in a season. Heat finishes the job, because PLA softens near 55 to 60 C and a dark print in direct sun can reach that on its own. PETG survives both better, holding to about 70 C and resisting UV longer, per the Bambu Lab and Polymaker PETG guides. ASA goes further still, holding its shape to near 90 C with a UV-stable chemistry made for exactly this job, per the Prusament ASA datasheet (HDT 86 to 93 C).

Choosing between ASA and PETG

Print ASA when the part sees real sun for long stretches, because its UV resistance is the whole point. The trade is an enclosed, heated printer and some fume handling, covered in the ASA guide. Print PETG when the exposure is mild or sheltered and you want an easier print, since it runs on almost any machine. The PETG guide and the ASA vs ABS comparison break down the printing side. For the broader material field, the filament overview places these in context.