[arghwhat]

A good example for the discussion: leather being animal skin which obviously cannot come from a mushroom.

Assuming you were countering my vegan leather claim: Products marketed "vegan leather" is polyurethane or similar, and for marketing reasons you would use a different term if you did something fancier to differentiate. My gut feeling is that a mycelium-based product would be far more expenisive than simple polyurethane, and quite an upsell.