Hmmmm I buy warm and natural and it states that it is cotton batting... I never read the whole label though, I will next time I buy it.
I googled polyprp and it is a polymer that is used as a fiber because it dyes well and doesn't absorb water. It is also used as a plastic for dishwasher safe dishes and can withstand heat up to 320 degrees.
So I don't know about using it for potatoe bags, I would think it may get hotter than that. Also, plastics not made specifically for microwaving, can leach out a poison/chemical of some kind. Interesting...