I have been using PET tape on my heated bed for a long time now. It works very well as long as I clean it with acetone about every 100 hours. It does need a high temperature (145°C) for the first layer with some types of ABS though .
It seems to last forever, the only failure mode is that large thick objects with sharp corners can defeat the adhesive and raise blisters at the corners near the edge of the bed. I solve that by building little heat shields to keep the corners warm. I am always on the lookout for something better though. It would be nice to get rid of the lines where the tape butts against itself.
A friend gave me a sheet of 1mm thick PETG to try. I clipped it onto my heated bed, and thinking it would behave like PET tape, I ran a build using the same temperatures.
Big mistake, PET has a glass transition at 75°C so it went soft and floppy. The object stuck to it very well and was hard to remove, but after getting a knife under one corner, it peeled cleanly. However it left an impression in the PETG.
The base of the object is flat but the filaments are more ridged because they sank into the sheet rather than being squashed.
When the sheet cooled down it warped badly, so that was the end of that experiment. I did have a small offcut though so I tried again at 70°C.
This time the object warped badly. It stayed stuck to the PETG but it warped the sheet. The adhesion was less and the object was easily peel-able. The PETG warped where the object was but the rest of it stayed flat. The heat of the object must have been enough to tip it over its glass transition locally. It left an impression, but not as deep as the first time.
The filaments on the bottom were squashed tighter, not as smooth as when using tape.
So a failed experiment. It is a shame because at high temperatures it bonds very well but, unlike PC, it still peels, but it is no good if it doesn't remain rigid. Wikipedia does say that PETG has a lower melting point than PET. It doesn't mention how it affects Tg, but it gives the Tg of PET as 75°C. Odd then that PET tape doesn't go soft at 75°C. My next trial will be Mylar, which is another form of PET (BoPET).
