Here's the footwear I use when the temperature is below 20 F (-6.7 C):
- Tingley rubber overboots, model 1400, height: 10 inches, cost: $21. Simply buy the size recommended by Tingley as if you were putting them on over your shoes.
- Gaiters to keep snow out of the boot, duct tape or old wool socks with the foot cut out are an alternative option
- NEOS 10 mm thick insole for non-compressible insulation from ground, cost: $5
- Steger mukluk wool felt liner ("mukliner"), cost: $17
- 1 pair Wigwam wool/acrylic socks stuffed into top of foot/ankle area for snug fit (optional)
- 1 pair Thorlos heavy wool trekking socks worn on foot
- oven bag used as vapor barrier (hoping to make silnylon socks), $3 per pair
- polyester dress socks or polypropylene liner socks inside oven bag for a liner
This is a waterproof mukluk approach. Besides being warm from insulation layers, it allows for excellent blood circulation in the feet. In fact, it even stimulates it because the feet flex and use foot muscles not used when strapped to a rigid sole.
Not counting gaiters, socks, and vapor barrier, this footwear system weighs 22.5 oz (1 lb, 6.5 oz or 638 g) per foot! This isn't bad at all because the average trail runner or hiking shoe in my size (10) weighs 16 oz.
Using a vapor barrier is important. Without it, the insulation layers will become soaked from sweat and ineffective due to the waterproof outer layer keeping moisture inside. Because they're essential but light and cheap, carry an extra pair of oven bags for every 2-3 days of the trip.
The extra socks I use to stuff the boot for a snug fit are oversized. This allows me to wear them over the other socks without circulation-reducing compression if additional warmth is needed.
An additional advantage is that the soft rubber boots have amazing grip on ice, and the sole's flexibility allows the feet to feel the ground, allowing for walking in snow without feeling like your feet are sliding around underneath you.
At 16 F while hiking in 8 inches of snow, my feet were too hot! They even felt like I had electrically-heated boots on while standing still.
I also have a pair of Tingley overboots which are 17 inches high, and are useful when high water crossings are expected. These add an additional 8 oz per foot.
- These boots are natural rubber. This gives them superb flexibility in the cold and great traction on ice, but they also break down quickly when exposed to oil or salt. Rinse them and coat with a rubber conditioner often.
- Carry heavy-duty duct tape such as Gorilla Tape for emergency repairs to cracks or punctures. Also carry a spare pair of turkey-size oven bags to use as an outer waterproofing layer in the case of an unsealable puncture.
- These will not work in mountaineering situations where sturdy boots are required for crampons or kick-steps.
- Sizing is not precise, and will need to be done through trial and error and extra socks or pieces of old socks to stuff into loose areas. Plan on returning or exchanging overboots and liners until you get the right fit.
Update Jan. 22, 2011: I replaced the wool felt insoles with 10 mm thick EVA insoles made by NEOS because they're less compressible. While snowshoeing and walking in 4 inches of snow for several hours, my feet were comfortable at 0 F (-17.8 C). I estimate this footwear system will keep my feet warm down to at least -20 F (-29 C) when active.
Update Feb. 6, 2014: A month or so ago, I was able to test this system more. While taking an extended time to pitch a 2 person tent and tweak the setup, my feet were comfortable at -10 F (-23 C) with a -32 F (-35 C) wind chill factor.
My next experiments will be with reflective insoles and liners.