I recently bought the large version for our 2 border collie pups aged 7 months, they are a total waste of money. The outer fleece cover flatens in 1 day, the inner thermal is actual a foil sheet with a backing,this is actually not fastened in any way to the outer cover,so when your pup/dog constantly moves about to either place their scent on the bed - its new so all dogs will do this before lying down or even when your pup/dog turns round and round before getting comfy, the inner foil/thermal layer crinkles up and has to be flattened again or if its a pup,they hear this crinkle and thinks its a toy so start playing with the pad, ours lasted 48 hours before it was totally flattened/chewed and ended up in the bin. the outer fleece is not very thick either. My advice buy a proper bed or one of the top name vet beds, they are better quality. The actual foil that is inside is what is covered to cover an accident victim to stop them from losing body heat and prevent them from going into shock.