These socks are made of lightweight merino wool, which insulates well in all conditions and won't crowd out space in tight fitting shoes. I've worn these on several hot long rides, and my feet never felt clammy. The high cuff provides good heel support-snug but not too tight. For reference, I wear size 42.5-43 shoes and the medium size socks fit perfectly.
These have quickly become my go-to socks. So comfortable in all kinds of weather, not bulky at all. Not itchy, either. I have size 11 feet, and these guys fit a bit small, just perfect for me. Nice compression without pinching at the top.