Two materials in one print raises a question single-material printing never does
Multi-material and multi-color setups, or simply printing two parts meant to fit together in different materials, raise a question that single-material printing never does: will these two plastics actually work together? The answer depends heavily on what "work together" means for your part. Two materials that need to bond at a shared interface face a real chemistry and print-temperature question; two materials that just need to sit next to or fasten onto each other do not.
How the check works
The tool first asks what you actually need: a bonded interface, or simply coexisting parts. For coexistence, material compatibility is not a real concern and the tool says so plainly. For a bonded interface, same-family pairs are the reliable case; pairs in a similar print-temperature band get a cautious "test a sample first" recommendation; pairs in different temperature bands are steered toward mechanical assembly instead of a direct co-printed bond, since dissimilar-temperature materials often do not adhere reliably to each other.
Worked example
PETG and ABS/ASA at a co-printed interface, needing real bond strength: PETG sits in a medium print-temperature band and ABS/ASA in a high band, a real mismatch, so the tool recommends switching to mechanical assembly (fasteners or an interlocking joint) rather than relying on the printed interface to hold.
A common mistake
A frequent error is assuming two materials that print at similar temperatures will automatically bond, when temperature band is only a rough proxy for actual chemical compatibility. PETG and PLA, for example, sit in a comparable range but do not reliably fuse at a co-printed interface. Always confirm with a small sample rather than trusting the temperature-band signal alone for anything load-bearing.
Limitations
Print-temperature band is a rough proxy for adhesion compatibility, not a measured bond strength for your specific brands and settings. Some printers and slicer profiles are tuned for specific tested material pairs that this general check would flag as risky; treat a positive result here as promising, not proven, and test before committing a part where the bond matters.