Its not just the leather itself, but the way you grow and tan the leather. Feeding a cow takes alot of grass, and in turn alot of land, fertiliser, water, sometimes pesticides (rarely), etc. As for tanning, cheaper and more common chrome tans are incredibly water inefficient and release pollutants into the air and toxic chemicals into local waterways.I don’t understand the use of sustainable in the title. Leather is an organic product made from animals that reproduce organically. How is sustainable here used t differentiate from normal animal leather which is …sustainable and been with humans for millennia and will be with humans for millennia. I think it makes sense to say fusion is sustainable vs coal (which might run out in 1000 years) but between two natural products I don’t get it.
Cactuses being a succulent take less water, less cultivated land for growing space, and have basically the same if not more benefits than animal hyde leather (breathability, patina, degradation after use, strength, etc).
Just because killing animals for skin is "natural", it doesn't mean it is sustainable.