To make sure that lost mittens don't jeopardize the trip, Frank emphasizes the need for more than one pair of shells and multiple spare liners. Make sure that circulation isn't cut off but at the same time dexterity isn't compromised too much. You have a whole sack of dry mitts but if it falls in a crevasse or gets blown away, you're going to need everything you have. Frank moves on to talk about feet, beginning with the story of a guided client who left his inner boots on for five days and got frostbite on his feet. Frank suggests sizing boots a little bit bigger, especially if using a closed-cell, or alveolite, foam liner because of expansion at higher elevations.
Circulation is vital, the feet are one of the first places to get cold.
Black Diamond, the US distributor of Scarpa Inverno plastic boots recommends going one shell size larger than would be used with standard liners. They keep your feet a lot warmer. Because your inner boot is dry, the outer socks are dry and basically you don't have to sleep with damp socks on your chest. The VBL socks eliminate evaporative cooling from the foot and prevent moisture build-up on the inside of inner boots. It is recommended that synthetic liner sock be worn inside the VBL socks.