70 to 85 °C, with 80 °C a sensible default on PEI.
The unusual part is the direction of the problem. Almost every bed-adhesion question is about parts coming loose. With PETG it is about parts that will not come off, and about what they take with them when they do.
Why PETG bonds so aggressively
PETG chemically likes PEI and glass. At the top of its bed range and with a well-squished first layer, the bond can exceed the strength of the plate's surface coating — so removing the part lifts a patch of PEI or a flake of glass with it.
That damage is permanent and it is the single most expensive mistake people make with the material.
Three defences, in order of effectiveness
- Print the first layer higher. Less squish means less contact area and less mechanical keying. This is the opposite of standard first-layer advice, and it is correct here.
- Use glue stick as a release agent, not as an adhesive. A thin layer of PVA between PETG and PEI gives a bond that is strong enough to print on and weak enough to break.
- Let the plate cool fully before removing the part. PETG's contraction on cooling does most of the release work by itself; prying at a warm plate does the damage.
Where within the range to sit
Lower, around 70 °C, for small parts on a textured plate — enough adhesion, easy release. Higher, near 85 °C, for large flat parts where the base needs to stay put through a long print.
PETG contracts 0.2 to 0.6%, more than PLA and less than ABS, so a large PETG part does have a genuine lifting risk that a warmer bed addresses.
What the bed cannot fix
Wet filament. If the first layer looks bubbled, sounds like it is crackling, or lays down unevenly, no bed temperature will help. Dry the spool at 65 °C for 4 to 6 hours and try again.
Build-surface behaviour across every material is in the bed adhesion guide, and the nozzle half of this question is answered at PETG print temperature.