Arctis Expe by Koflach is the warmest boot made. It is a great choice for technical ice climbing and general mountaineering. The lower part provides rock-solid stability with step-in crampons while the opper part pf the boot flexes nicely for hiking. This boot which retails for $360 is in great condition and has been only on Denali for about 3 weeks. These boots have been to the summit and back.