All Acton winter boots styles are associated to a comfort zone. The following comfort zones were scientifically determined based on the number of thermal units (B.T.U.) needed to keep the interior of a boot at a comfortable temperature, and thereby meet your specific needs. Factors such as the person's physical condition, the type of activity and its duration, the humidity level and fit may affect comfort. Moreover, it is very important to use quality synthetic fibre socks, like polypropylene socks. Take good note that clean socks offers more thermal qualities.