I just moved this to its own topic so it wouldn’t get lost.
There’s a lot here, but the short version is that we spent a long time trying to create good advice that would allow a nontechnical person to safely use materials from unknown suppliers. We concluded that we couldn’t. The only advice we could give that would result in safe (nevermind reliable) operation would be frustratingly complex at best and misleadingly dangerous at worst (because there are supplier problems that are undetectable without expensive equipment). Further, we decided that we, Glowforge, didn’t have anything particularly helpful to add to the already-large online body of knowledge about selecting materials for CO2 laser processing.
Ultimately people want to hear this from us because they trust us to provide simple and accurate information, and there isn’t any information about this topic we think is both simple and accurate.
So we decided to focus our energy on where we actually could produce a great, safe, reliable experience - Proofgrade materials.
To answer your question about the warranty: if your unit is damaged by Proofgrade materials, it’s covered by the warranty (although that is improbable). If it’s damaged by material you provide, regardless of where it came from, that’s not covered under the warranty. We recommend Inventables and Laserbits, but if they send you PVC for some crazy reason, the resulting damage to the Glowforge isn’t covered under warranty, nor is damage caused by you putting in a piece of polycarbonate and melting it all over the crumb tray.