Thermoplastic polyester PET, which should not be confused with normal thermoplastic polyester, is distinguished by its impact resistance (comparable to polycarbonate). As a partially crystallised plastic it will not break even after being bent a million times. PET is extremely resistant to fatigue and functions excellently as a joint which will not whiten at the bending point - a 0.5 mm thick sheet will tear after being bent a 100 times to 180¡ in both directions).PET is absolutely colourless and has very high light transmission. The sheets are not really suitable for long term use outdoors because they will yellow under the influence of UV.