Those white, quilted, slightly padded, washable things (not the waterproof ones!)
I used to have some that were polycotton. Got some newer ones, they have a backing of polypropylene, which melts in the tumble drier. I have looked at Silentnight, and own-brands at Tesco and Sainsbury, they now have polypropylene as well.
Does anyone know a brand that doesn't, and will stand up to tumble-drier?