PUL is the waterproof fabric that is used for making diaper covers. I purchased some at JoAnn's to use as the inside of a travel tote/make up bag. It is 100% washable and feels like fabric, unlike the vinyl covered fabrics and laminates. Check
www.byannie.com and look at the Soft and Stable. I think it would work very well with a layer of insulbrite to give your bag shape and body. I used it in a purse and the sides didn't droop and collapse like they would have with just an interfacing.