The Salomon Tundra Mid WP insulated boot probably has the highest warmth to weight ratio to be found anywhere. It's insulated with Aerogel, which was developed by Aspen Aerogels for NASA, and is claimed to have the highest thermal insulation value of any solid material available. Aerogel is a silicon-based solid with a porous, sponge-like structure in which 99.8% of the volume is empty space. It's one thousand times less dense than glass, which is another silicon-based solid. Aerogel is not like conventional foams, but is a special porous material with extreme microporosity on a micron scale. The individual pores are only a few nanometers in size. A nanometer is one billionth of a meter.
This boot was initially introduced in fall 2007 as the Aspen, which was significantly taller (11 inches in back, 12 inches at the side). The Aspen was replaced by the Tundra in fall 2008, and the new boot measures 9.5 inches at the back and 10 inches at the side. In short, the Tundra gets it right (read my comments in the following section).
The Tundra is nicely designed, and is constructed of very durable materials (see specifications table). The uppers are all synthetic, with a very durable molded rubber/fabric (like Hypalon) lower section cemented to the outsole. Both the toe and heel have rugged bumpers for extra durability, and the heel has a notch for snowshoe and crampon straps. The grippy outsole has Contragrip rubber which remains flexible in extreme cold temperatures.
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