PETG or PLA

[Modelworks]

PETG is my go to filament now. PETG doesn't crack and tends to bend instead of breaking.
I can take pliers and twist parts I make without breaking them, they deform of course but do not break.
It is not as hard as PLA but pretty close. I use it outdoors, on my CNC for clamps and parts, printer, etc.

I tried printing at higher temps 230C + and found it to be brittle then started using 216C with a 50-70C bed temp and good cooling for bridges and it works great.
I chose the temp based on starting at the point where it just starts to flow out the nozzle easily and then increasing it a few degrees until the layers were strong enough to not de-laminate.
Too hot it was a stringy mess and brittle and too cold it jams the nozzle. Cooling it quickly made a difference in strength as well.

I did some research on why PETG temps may be more critical than other filaments.
PET is the plastic used in soda bottles. It is resistant to water, alcohol and most solvents. The problem with using it for printing is it has a high melting temp so to lower the temp they add glycol. The process of adding the glycol happens at about 250C , not much higher than extruding temp which may be the issue some have with breaking of filament.
The original product is from the 1960's and was known as KODAR created by eastman kodak.
From some patent docs:

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.

[airscapes]

Great info!! Thanks so much for posting that!
What do you use on the bed? I use polyimide tape on my build plate.. just wondering if the PETG will release. Freezing PLA with can air propellant works great but with PETG I would guess it will not due to it temperature stability? Does glue stick work with PETG? I like the idea of just running the plate under water removing the glue and part..