Quote:
KODAR PETG 6763 material can be injection-molded at temperatures above 390° F.. However, at temperatures of 420° F. and above, the material degrades, making it brittle. This results in a difficult injection-molding process, since the molding range is quite narrow. Also, at the low end of the molding range or below, the plastic becomes brittle because of molded-in stress.
Apparently over the years different formulations have been made to make the temperature window wider , so you need to test temperatures with your brand of filament. The window is narrow for what is good or bad but once you find the right temp PETG is a great filament. If it cracks you are too hot and if layers separate you are too cold.