Socks that are cool in the summer and warm in the winter, how can they be both? The answer is evaporation.  As bamboo viscose fibers pull moisture away from the foot and towards the outside of the sock, it interacts with air where it evaporates.   As moisture evaporates, it draws heat leaving the surroundings cooler. In the winter, the same evaporative cooling process occurs but it helps to keep you warm due to the the moisture removal. Moisture in direct contact with your skin will draw more heat than air so the less moisture the better insulated your foot is.  Many Ecosox styles incorporate rows of pillow cushioning in the sole that creates air gaps. These air gaps work with the viscose fibers to enhance the evaporative properties and increase the performance of the sock.  Learn more about babmoo here.  Bamboo is better   Shop All Socks