We're currently trying to choose the material for the sides of the akkupack project, and due to laser-cutting Aluminium being not quite expensive, but still costing a considerable amount, we're looking at alternatives.
Acrylic would be one suitable candidate, though the brand-name acrylic costs around 40€/m².
I still have some Kraftplex (pressed cellulose fiber) around and we did some very unscientific stress testing on that. It unfortunately doesn't quite make UL94.
In the end it might not even be flammable at all under the standard conditions.
The only worry i still have is, that it's technically deformable with water, but just soaking it for a minute did not yield any meaningful results on the 3mm thick sample, so it might just be that this won't be a concern either.
The social network of the future: No ads, no corporate surveillance, ethical design, and decentralization! Own your data with Mastodon!