@TazPoltorak I'd be quite wary of polar fleece (and synthetic wadding) melting at oven temperaturesif you have some wool scraps they may work instead of the thermo insulation, but maybe you'd need a bigger thinkness, and with cotton you'd definitely need more than either.

@TazPoltorak it has a texture that some people (including my mother) hate, I don't know whether modern linen is smoother.My experience with bamboo/viscose is that it feels very nicely cool at first (and it's very nicely smooth and silky), but linen is better at keeping cool during the night.Also, I'm using the linen bedding on top of a cotton mattress, and right now my partner¹ is using a wool mattress, both also help compared to sleeping on plastic.

@TazPoltorak ooooo, what are you making?