PETG is one of the most commonly used filaments. It is an excellent choice for printing mechanically stressed parts. Compared to PLA, it is more heat resistant, more flexible and less brittle.
The G in the acronym PETG stands for Glycol which is added during the manufacturing process. Glycol modifies the properties of PET, so that it’s easier to print, less brittle and clearer when printing with semi-transparent variants. PETG has a low thermal expansion, so even when printing big objects, and without an enclosure, it rarely lifts from the bed and warps. In addition to that, PETG is ductile. It has a healthy amount of flex which can prevent parts from breaking under pressure.