The most asked question when people shop for winter or mountaineering boots is “Which boot is the warmest?”
The answer is as simple as the question but there are many factors that contribute to both actual and perceived warmth. First consider that boots are not subject to any standard test or certifications however manufacturers generally make their models adequately warm for their intended use and conditions. Have faith that today’s winter, ice and expedition boots are some of the warmest ever and base your boot choice primarily on fit, comfort and the type of climbing you imagine you will be doing. External factors that greatly affect foot (and hand) warmth include general health, hydration, circulation, diet, rest and genetic predisposition to the effects of altitude. The mountaineer who regularly works out (especially cardio training), eats (and drinks) wisely, works some hot sauce and chili peppers (capsaicin) into his diet, supplements with ginkgo biloba on the trip, takes rest days and is able to get regular, good sleep will likely also have warm fingers and toes.
Climbers with a history of compromised circulation such as Reynauds Syndrome or suffer from chronic cold fingers and toes can condition themselves to deliver more warm blood to their extremities. In the fall, before ice climbing season kicks in or weeks before your expedition, strip down to your underwear, fill a bucket with warm (not hot) water and treat your feet and hands to a bath for about 10 minutes a session. Do this immersion exercise outside in the evening’s chill every day for about a week (if you live in Texas, you may need a walk in freezer). Fingers and toes that were once blue or white after only a pitch or two may surprise you may becoming warmer and more workable.