PLA and PETG generally do not bond strongly to each other. That can be turned into an advantage: print the model in one material and use the other only for the support interface. The interface can support the surface closely while still separating after printing.
Why use only the interface?
Printing the entire support structure in the second material creates far more tool changes. Using the second material only for the dense contact layers usually keeps the mechanical benefit while reducing time and purge waste.
PLA model with PETG interface
This is a common combination for difficult undersides. PETG can form a close support surface beneath PLA without fusing strongly to it. Start with conservative temperatures and a small test part before committing to a long print.
PETG model with PLA interface
The reverse combination can work as well. Cooling behavior and temperature transitions are different, so toolchanger systems with separate hotends are generally easier to tune than single-nozzle systems.
Top Z distance
A zero or very small Z gap can be possible because the materials themselves act as the separation layer. That does not mean zero is always best. If the interface fuses or the underside becomes rough, test a small positive gap.
Interface layers and spacing
More dense interface layers can improve support quality but cost time and material changes. A very dense interface may be unnecessary on simple geometry. Tune the number of layers, line spacing and pattern together.
Purge contamination matters
If too much PLA remains in a PETG interface line, or vice versa, the layer may bond differently from expected. That is why purge settings can affect support removability, not just color purity.
Toolchanger vs. single nozzle
Toolchangers keep materials in separate melt zones and avoid repeated full melt-path exchanges, but inactive tools can ooze or restart under-primed. Single-nozzle systems need stronger purge control because both materials share the same hotend.
Start with a small calibration model
Use a part with a flat supported ceiling and a few curved or angled surfaces. Test removability, underside finish and purge contamination before using the profile on a large print.
