Review on Lipport Waterproof Cycling Shoe Covers: Stay Warm and Dry with Thermal Shoescover for Men and Women, Perfect for Road and MTB Biking by Frank Webster

Protects against the wind and keeps you warm. So far I've been in my high 30's and with 2 layers of socks my feet stay warm on the inside. I wear Shimano MTB shoes with large mesh vents on the top for summer rides and on cold rides my vents freeze very quickly. With these covers, they will now stay warm much longer. Keep in mind that they aren't super insulating and won't keep you warm when you're not active. The cold temperatures will eventually pass, but they are designed to protect feet from wind and water and they do the job very well. They fit my size 47 MTB boots very well (I bought size XL) and leave enough room for the cleats and MTB tread. They stretch well and attach with Velcro in the arch area of your shoes. The zipper on the back makes them very light. Edit: Went outside in 35 degrees and got caught in a downpour on the way home. It was a 40 minute drive home in the rain and my riding boots stayed warm and dry!