Smartwool socks are made from a special New Zealand wool. The nice wool makes the sock extremely warm but comfortable at the same time. The wool also contains a lot of air bubbles which help keep your feet warm dating the winter while cooling them down in the summer. This comes in handy during the winter in places like Boston where you can be outside in below zero temperatures and walk into a heated building. The air bubble contribute to making a very breathable sock as well, making these ideal for active people or someone playing sports(Hiking).