I’m happy to see that community members have already mentioned the very helpful Beyond the Manual section.
With regards to printing on materials provided by other vendors, unfortunately, I don’t have any guidance. It’s very common for materials to perform inconsistently in a laser. However, Proofgrade materials should print perfectly every time. Should you find a problem when printing on them, please let us know right away.
If you want to see if the community has suggestions about materials and/or material settings, you can post in Beyond the Manual. Note however that advice in this section is unsupported and is not reviewed by Glowforge. I’m going to go ahead and close this topic.