How do I, as a naturalist spending a lot of time outdoors year-round, keep warm on cold winter days? I take some cues from animals that stay active in the fields and forests around us.
Let’s start with some heat and cold science. Heat moves from areas that are warmer to areas that are cooler. There’s no stopping it. Heat migrates away from our bodies in four different ways:
Conduction — heat escaping through direct contact. When you touch that cold car door handle, having forgotten your gloves, the heat is conducted from your warm hand into the cold metal.
Convection — heat loss by moving air. That biting wind hits you and cuts right through your sweater and you shiver as your skin feels the chill.
Radiation — heat waves leaving your skin. You step out of the house without a coat and stand there watching the sunset on a cold, still, cloudy evening, and you feel colder and colder.
Evaporation — liquid water turning to vapor taking away heat. As you come back from a brisk winter walk, a neighbor catches you and wants to talk. Standing there, any perspiration built up during your walk evaporates, taking body heat with it.
Our job, then, is to slow the rate at which heat escapes from our bodies. We can’t prevent the loss. But we can slow it down so that the heat our body produces equals or exceeds the rate at which heat escapes us. And, take it from chickadees, grouse and deer, insulation is the best way. Not fiberglass or rigid foam or cellulose, like we use in buildings, but insulation just the same.
Now this may seem counterintuitive, but air is a very good insulator. Heat moves across a layer of air very slowly — as long as the air isn’t moving. So still air is what we want. How do we surround ourselves with still air? We capture air in little pockets held in a matrix — like the chickadee’s feathers and the deer’s hollow hairs. We use wool or down or polyester or thinsulate or fleece. Designers keep developing new matrices to hold the air pockets, but the physics remains the same.
The next principle of keeping warm may not be received well by some people because contemporary fashion often dictates tall and slim; but keeping warm flips that: thick is cool! The thicker the layer of pockets of air around you, the slower heat will escape and the warmer you will feel. This thickness is called loft — the distance between your skin and the outside air. You want to maximize loft. You’ll probably look roly and poly — the new tall and slim.
One way to increase loft is through layering. You may have heard that more, thinner layers are better than one big coat or sweater. With thinner layers, the air pockets within each garment hold the heat, and there are also air pockets between the layers for added insulation.
When I am outdoors, below freezing, for hours, I wear a T-shirt, a turtleneck, three wool sweaters of varied weights, a hat, gloves and a down parka. If precipitation threatens I include a water-resistant outer layer. I wear woolen long underwear all winter. And I am warm — REALLY! — for hours. My feet, hands and head keep warm, because heat loss has been greatly reduced and is constantly replaced by my body’s metabolic furnace.
Strong winds can penetrate layers of air pockets unless we stop them. Tightly woven fabrics of ”windproof” materials prevent the wind from reaching into our air layers. These materials help in slowing heat loss. Find a good outer layer that is windproof.
But there’s another ingredient in the keeping warm balance. It’s just as important to life as air. Water, unlike air, conducts heat readily and evaporates very successfully — so it works to keep us cold. Keeping yourself dry will help tremendously in keeping warm. Water-resistant (but not necessarily waterproof — see below) outerwear in rain and snow is essential.
If you’re active in the cold you will most likely sweat. Sweat will seek to evaporate into the surrounding air, thus cooling us. But there’s a solution to this problem. Wool and some other fabrics are good at wicking — moving moisture away from the skin toward the outer layer of covering. This way when the water evaporates it isn’t taking heat directly away from your skin.
This is why we talk about breathable fabrics. These garments prevent the passage of water in toward the body from outside, but allow air to pass out away from the body, carrying any build-up of moisture away from our skin. Breathability is good — as long as the material continues to exclude rain and melted snow from entering. It turns out that waterproof isn’t best, after all, because our body’s moisture, passing through our skin, needs to escape.
Grouse, deer and chickadees have come up with heat conservation systems that work. Studying their adaptations to the challenges of winter cold offers design solutions to our own warm-blooded heat loss problem. Spending time outdoors in winter can be glorious and comfortable if we dress for it. I hope to see you out in the snow!
Ted Watt is an educator/naturalist at the Hitchcock Center for the Environment. His Earth Matters column for Dec. 16 describes animal adaptations for surviving in winter. Learn more information on the science of heat loss and different fabric choices.
Earth Matters, written by staff and associates of the Hitchcock Center for the Environment at 845 West St., Amherst, appears every other week in the Daily Hampshire Gazette. For more information, call 413-256-6006, or write to us.