Why are my feet cold? And what can I do to keep them warm?

Gaerne Winter Road shoes

Now that winter is really upon us, I've started hearing a lot of chatter about cold toes and feet. If you want to keep riding outside through the winter weather, having a strategy to maintain warm hands and feet is essential. Freezing cold fingers and toes can quickly ruin or cut short an outdoor ride. The risk of frost bite is real!  

To achieve warm feet, it helps to have an understanding of why your feet are cold. For the most part cold feet are due to the following factors:

1. Poor circulation
2. Wrong footwear and/or socks
3. Moisture
4. Heat transfer, convection and conduction.

Lets look at these in order. 

• Poor circulation.  Some people just don't have good circulation to their extremities. These people will be the first ones to say their hands or feet are cold. When temperatures drop your body thermoregulates by sending more blood flow to its core. Protection of vital organs comes before extremities.  Ever read "To Build a Fire" by Jack London?  The hunter knew that he might lose parts of his foot or toes to frostbite, but that he could live if he could make into camp.  One strategy to keep your hands and feet warm then is to make sure your core is warm. This means eating enough fuel before and during the ride, hydrating well to ensure good blood pressure and circulation and dressing properly so that your core stays warm. If your core is heated well, your body's thermoregulation systems will continue sending blood flow to the surface and extremities. When it goes below 35 degrees, I recommend a long sleeve base layer, a fleece long sleeve jersey and winter jacket. For the lower body, I've worn fleece bib knickers with a layer of winter tights on top. And long ski socks. 
• Wrong footwear. Your standard bike shoes are designed primarily for summer riding. In fact their design includes mesh and venting to let out heat and moisture. This is great for warm weather riding, but it will work against you in cold weather. As temperature drops into the 50s you can add toe covers, which work well, as temps hit 40 you may need a full bootie. The other problem with your summer bike shoes is that they are designed to be worn with a thin summer sock and be snug on your feet. If you now try wearing them with thick winter socks, you may find that your shoes are tight and that will restrict circulation in your feet.  All booties have a cut out on the bottom for the cleat and cold air will come in through the opening.  If you plan on doing a lot of winter riding, I would recommend a winter shoe.  The advantage of a winter shoe is that (a) it is insulated, (b) it does not have venting like a summer shoe and (c) it is build wider and roomier, to accommodate thicker socks without restricting your circulation.  The better winter shoes use Windtek fabric on the exterior, are water and windproof and have thermal insulation built in. If you buy a pair, they will last 5-10 years because you will only use them a few months out of the year. They come in road or MTB versions.  You will never again have to fuss with putting booties on.
• Moisture is often overlooked, but feet do sweat and get damp. If you wear booties, you will see the moisture when you get home and take off the booties. This is water vapor that leaves your feet and condenses upon meeting the cold air outside. The key here is the right kind of sock. Cotton socks are the worst, the absorb moisture and will be very cold when wet. Wool is the best, it will retain its insulating property even when wet. Some people like silk sock liners, which will carry moisture away from your feet to the outer sock. 
• Heat transfer.  Your feet are producing heat, but that is balanced with heat loss. The colder it is outside and the more frontal wind, the faster the heat loss.  Heat will be conducted away from your foot through direct contact with the sock and inside of the shoe. One of the keys here is to have warm air spaces in your shoe (i.e. shoes not too tight), because air is not a good conductor of heat, you will reduce heat loss if your shoe is more loose and has enough room around the toes.  Convective heat loss will be very high on a cold windy day and the only real solution is enough insulation and windproof fabrics.

What about supplemental heating? If you've tried all of the above and still have cold feet, you may want to try supplemental heating in your shoes. This can either be a chemical warmer (hot packs) or a battery operated footbed.  The chemical warmers are sold at Home Depot and Outfitter stores. You can attach the toe warmers to your sock or insole and I've found that these will produce heat for 3-4 hours. Some people put them on top of their toes, I've always thought that they work better under the toe.  There are also heated foot insoles available, one is the Thermacell, which cost around $100 and use a lithium ion battery built into the footbed. Some reviewers liked these, others said they didn't heat well. The Hotronics system used in ski boots is probably the best. If you already have Hotronics in your ski boots, you can buy another set of heating elements and footbeds for about $40. You can use your existing battery packs, although you will need another set of clips. Aside from looking silly having the Li-ion batteries attached to the back of your winter shoes, you will have adjustable heating that will definitely keep your toes warm even on the coldest of days.