I usually wear an 8 in the Encore clog, so I ordered an 8 and 8 1/2. Kept the 8 1/2. Ordering a whole size up would be too large in the heel. They are really waterproof, I wore them for the 1st time in NYC in the pouring rain and my feet were as dry as a bone and I walked over 20 blocks. I can't comment on the warmth factor yet, because it was 50 degrees. Some facts that might help you decide the right size: Not much toe room even in the 8 1/2, doubt a heavy sock could be worn, unless you are a narrow width. The toe was wide enough, but definitely not enough wiggle room, as in the Encore style. I wore with trauser
socks. The heel area is wide in comparison to the toe, and the
boots slip a little in an up and down movement...maybe heel is wide to allow for pull-on, as there is no zipper. Since I knew I would be walking a lot and this was the first time wearing them, I used mole skin on my ankles and that worked. I'm hoping they will break in and i don't plan on walking 20 blocks again anytime soon! All in all, I would recommend them. My advice is order two sizes and keep what fits best.