UV resistance: how a 3D print stands up to the sun

What UV radiation does

The sun also emits ultraviolet radiation, which breaks the bonds in polymers. This process is called photodegradation. The plastic gradually changes colour, its surface changes (chalking) and it becomes brittle. The speed depends on the material, the colour, the intensity of the sun and the temperature.

PLA, PETG and ASA

PLA is fairly stable chemically in the sun, but heat is the problem: it softens at around 60 °C and outdoors in summer there is a risk of deformation (glass transition). PETG is the better choice, as it holds up to heat and damp and keeps its properties longer. ASA was developed precisely for outdoor use and keeps its colour and surface in the sun longest, but we do not print it.

Dark parts heat up more in the sun. Light and white ones are thermally safer, but can yellow.

What to do with outdoor parts

For parts permanently exposed to the sun, a stronger infill brings nothing, as it is a property of the material. With PETG, expect that after several seasons it may fade and become brittle, but not within a week. A coat of UV varnish helps, but we do not do coating, and you can have it done yourself.

If it is something important, such as a bracket on a facade or part of garden equipment, rather order one extra as a spare and check the part after the season.

What we suggest

We print only PLA and PETG. For outdoor use PETG is a close alternative to ASA, but not an equal one. If you need a part to last for years in a yard or on a car, write to jakub.novak@boostello.com and we will tell you what can and cannot be done. We cannot promise to print ASA.

Practical tips for outdoor parts

For outdoor parts we choose light or mid colours, which heat up less in the sun. Dark black or blue heats PLA and PETG a few degrees more and they soften sooner. Keep in mind too that heat and UV act together: a hot sunny day is worse for PLA than a frosty one.

If the part matters, run a test: put a sample for a few weeks where it will be used and see whether the colour or surface changes. Cosmetic changes usually appear first, that is a faded colour and a matte surface, and only later brittleness.