Size 3-8 UK (marked on the packaging), knowing that the size UK 9.5 corresponds to the 44 here! So too small for me, they could say so in the description anyway ... Okay, it's a gift for my mother. I still unwrapped to test the heater before offering (not want it burns ^^). 1min30 in my microwave, diffuses a pleasant heat for a little less than an hour. Not surprisingly, I have not been able to drag their feet, the elastic at the ankle is too tight for me, I think it is for people making up the 40.