Purchased these for fat tire snowbiking and snowshoe racing. I only used the booties in one 24K Snowbike race (Noquemanon) so far, but I have only good things to report. I wear size 12 shoe and I bought the Gore booties for 13.5 to 15. They fit my shoe perfect. Temperature at race time was about 15 degrees and my feet stayed toasty warm from start to finish.