I got caught outside at sundown on a ride last week and nearly froze my feet off. I was dressed for the weather when I left but I never expected the temps to drop that suddenly. The rest of my body was fine but my bike shoes are well ventilated so my feet got cold pretty quickly. After that, I decided to get some shoe covers :) These fit the bill perfectly. I have a pair of Sidi Pro Carbon shoes size 46 and ordered the XL which fit perfectly. They could easily stretch over at least one size larger. I tried them out today which was in the low 40's with a cold breeze and they worked as advertised. I was out for about 90 min and my feet were nice and warm when I got back. Build quality is nice - they are mainly neoprene with some more resistant material on the toes and underneath and the stitching is solid as well. So far, so good.