PETG UV resistance is moderate, and the honest answer is a number of years rather than a yes. A garden centre in Kent used clear PETG for plant labels and bed edging in spring, replacing them every second season. By the third year the pattern was obvious: the labels were fine indoors, and chalky outdoors. Nobody had asked the question until the cost line became visible.
What PETG UV resistance actually means in service
Unstabilised PETG in direct sun develops a yellow cast within six to twelve months. The transmission loss is small at first, around 2 per cent, and the colour shift is what people notice.
By year three the surface has chalked, impact resistance has fallen sharply, and a panel that survived a knock in year one will crack in year three. That embrittlement is the real failure, not the colour.
- 0 to 6 months: slight gloss loss at the sun-facing surface
- 6 to 12 months: visible warm cast in clear grades
- 1 to 3 years: chalking, measurable impact loss
- 3 years and beyond: brittle fracture at impact points
What a stabilised grade changes
UV-stabilised PETG uses absorbers that convert the damaging wavelengths into heat before they break polymer chains. The result is three to five years of service rather than one, with slower colour drift and much less embrittlement.
It does not make PETG equivalent to acrylic outdoors. Acrylic holds clarity for a decade; stabilised PETG buys time.
Thickness and the exposure rate
A thicker sheet takes longer to embrittle because the surface layer protects the core, but the colour change is a surface phenomenon and appears at the same rate regardless of gauge. Thin sheet fails mechanically first; thick sheet shows colour first.
Where PETG outdoors is still right
Short-life signage, event structures, temporary glazing, protective covers that will be replaced on a maintenance cycle anyway, and applications where chemical tolerance matters more than clarity.
In each case the material is chosen for toughness and formability and the outdoor life is accepted as a consumable. That is a legitimate engineering decision as long as it is a decision.
Where it is the wrong answer
Permanent glazing, anything sold with a five-year appearance warranty, and any panel whose replacement requires scaffolding. In those cases the small saving on PETG is far outweighed by the second visit.
For permanent clear glazing, the UV resistant acrylic sheet note sets out the decade-long case. Where impact is the driver, the UV resistant polycarbonate note covers the alternative.
One practical test before committing to an outdoor PETG part: leave two samples outside facing south for a season, one with the protective film removed and one without, and compare against a retained reference. The result is more informative than any data sheet curve.
Tell us the exposure and lifespan you need at oversales@rpplexiglass.com; we will recommend a grade or a different material.
Frequently Asked Questions
Does PETG yellow in sunlight?
Unstabilised PETG yellows noticeably within six to twelve months of direct sun, and the change is visible as a warm cast in clear sheet.
Is there a UV-stabilised PETG?
Yes, grades with UV absorbers and stabilisers extend outdoor life to three to five years. They slow yellowing; they do not make PETG a decade-long outdoor material.
What should I use instead outdoors?
Acrylic for clarity over a decade, polycarbonate where impact resistance matters. PETG is best kept for indoor duty or short-life outdoor work.