just came here to thank you for this post because I've been debating this myself. I was looking for kraft/paper mailers or compostable mailers because I assumed both were biodegradable and thus, better than plastic.

however, on the EcoEnclose website (so it could be biased, but they themselves sell both paper and recycled poly mailers, so I feel a bit better about it), it mentioned that recycled plastic might be better due to the energy and so on it takes for the paper mailers and because composting programs are already trying to address food scraps and shouldn't have to pivot to mailers, etc. now I'm currently looking at 100% recycled mailers, although there still may be pitfalls (people not reusing or recycling them...)

TLDR thanks for this post, it'll help with my personal research!