PET (polyethylene terephthalate) is probably best known from plastic bottles used for soft drinks and similar containers. It is a rigid and hard material with strong interlayer bonding. PET is naturally transparent, but is also available in colored versions. PET has an increased tendency to make small strings when printing. Therefore, it is recommended to increase its retraction relative to e.g. PLA; However, as always with retraction, this is something you have to test with regard to the exact amount needed.
PET melts at 250-260 °C. A heated build plate is needed; it should be heated to 70-90 °C depending on what it is made of and whether you use tape, glue stick or something completely third to ensure adhesion.
PET filament is hygroscopic, which means it absorbs moisture from the surrounding air - it is therefore recommended to store the material in a drybox; a (mostly) air tight container with silica gel in to absorb moisture from the air. If your PET filament makes little popping noises when it is extruded, the reason is that it has absorbed too much water. This can be remedied by drying the filament in an oven with precise temperature control; such as a food dehydrator, or a dedicated filament dryer.
If you are considering drying it in a conventional oven, it is important to test the stability of the temperature as it can fluctuate quite a bit. This can lead to your filament fusing together on the spool.
Depending on how much moisture the PET filament contains, it is recommended to dry it for 8-24 hours at 65 °C.
Print at 40-50 mm/s
Do not squeeze the filament against the build plate
Requires a heated build plate
Store dry, preferably in a drybox