Outdoors, the deciding factor is ultraviolet light. A powder that performs flawlessly indoors can chalk and fade on a facade within months.
Epoxy powders offer excellent chemical and corrosion resistance but poor UV resistance — they're an indoor material and shouldn't be specified for exposed work.
Polyester powders are the standard outdoor choice. They hold colour and gloss under sun exposure, and facade profiles, joinery, railings and garden furniture are normally coated with them.
Where exposure is severe — coastal air, industrial atmospheres, high-rise facades — a super-durable polyester or a certified architectural system gives noticeably longer colour retention.
Colour choice matters too: deep, saturated reds and blues fade faster than greys, whites and blacks, so a more stable tone is usually the safer call for large sun-facing surfaces.