Our 3D printing process uses thermoplastic. This thermoplastic is called PLA (Polylactic acid), which is derived from natural, plant sources, typically from fermented plant starch such as corn, cassava, sugarcane or sugar beet pulp. It is considered a biodegradable plastic. We use premium grades of PLA, generally known as PLA+ or PLA Pro, for superior strength and durability compared with standard PLA.
PLA does not have a good tolerance to high temperatures. For this reason we recommend that all of our products that use lights, namely the lithophanes, use ONLY LED-type bulbs. LEDs provide more light with less energy consumed and much less heat generated.
PLA items generally do not fare well outdoors, especially when exposed to direct sunlight, since the sun’s rays will degrade PLA fairly quickly. Indoors, items made with PLA will last perfectly for many years under normal conditions.
More information on PLA can be found at this Wikipedia page.