I run a pet product business here in South Africa and we make our own dog/cat beds etc.

I make my own snake bags. I make them with a double inner, a strong fabric on the outside (Denim) and a softer fabric inside (Cotton twill/ sheeting) and tie straps. The bottom of the bag has a pvc base so if the snake pees it does not leak everywhere.

I too have had no casualties. I'd avoid using a waterproof material though, also I'd avoid very rough fabrics as these may irritate your balls.... he he...

For the purpose of snake bags I'd recommend plain fabric (no glitter fabric, fabric with sequines etc) which is not waterproof. I don't think breathability is too much of a concern as all no-waterproof fabrics allow air to pass through them...