Fifteen years ago on a February day when the wind chill was about 50 degrees below zero I turned 40 on the side of New Hampshire’s Mount Washington.  Almost every winter of the next decade, I climbed (or tried to climb) the highest mountain in the Northeast and twice I was beaten back by weather that made 50 below feel like spring.  Through these winter ascents on a mountain with the highest recorded wind on earth, I’ve learned how to dress for long days in tree stands when the mercury plunges.

Layers

            Layering is an art.  Piling on clothes until you look like the Michelin Man might keep you warm but it could also get you a role in the “I’ve fallen and I can’t get up” commercial.  Whether climbing or hunting, three layers of clothing is the optimum combination for warmth, comfort and flexibility as long as the layers are the right material and the right fit.

            Many years ago my young son asked me a question that showed the science behind layering.  He came out of my bedroom holding a wool sweater and a cotton shirt and he asked why people say wool is warmer when they both feel the same.  The answer is that wool is not warmer than cotton.  In fact, no material is warmer than any other material.  Wrap thermometers inside your thickest down jacket and your thinnest cotton T-shirt and a half hour later they’ll both show room temperature.

            The science behind that youthful question is that certain materials keep you warmer than others by slowing the loss of the 98 degree heat your body produces.  Proper layering maximizes heat retention by utilizing different materials in each layer to trap heat and by limiting your body’s ability to sweat it away.

Base Layer

            The base layer is the layer against your skin and its primary role is to keep your skin dry to slow the loss of heat.  The purpose of sweating is to cool us off because sweat pulls heat from our skin faster than air does so to stay warm it’s important to stay dry by “wicking” sweat away as quickly as possible.

            First, forget the waffle pattern cotton longjohns your grandfather swore by.  Mountain climbers call cotton the death cloth because it absorbs sweat and actually increases heat loss by keeping water against your skin.  Seven years ago a new guy I took up Mount Washington wore his cotton briefs under his high tech underwear and mid way up the final headwall a sensitive part of his body chilled so much that the first thing he did when we got down was throw the briefs away.

            A good base layer should be a synthetic material such as polypropylene, thermax or comfortrel that fits snuggly against your skin.  These fabrics draw (wick) sweat from your skin to the far side of the fabric where it can evaporate without robbing your skin of heat.

            Although any polyester fabric can wick perspiration, the best synthetics are woven from hollow core fibers to help trap your body’s heat.  Like the hollow insulation in your sleeping bag, the hollow threads in base layers slow the transfer of your body heat by forcing it to travel through a layer of dead air.

            To understand how this works, picture a storm window with two layers of glass separated by an inch of air.  The heat from your home escapes quickly through the first solid pane of glass but the dead air is a poor conductor of heat and it slows the transfer to the outer pane.  To really appreciate how poorly air transfers heat, ask yourself how long you could hold your hand in boiling water, which is about 220 degrees.  The answer of course, is not at all.  Now consider how long you can reach into a 350 degree oven.  The answer is quite a while as long as you don’t touch anything solid.  That’s because it takes time for the dead air in the oven to transfer the much higher heat to your hand and it’s why eggs cook faster in boiling water than they would in a hotter oven.  Hollow fibers keep you warm on the same principle.

Middle Layer

            The second layer is your heat layer.  High tech long underwear slows heat loss by wicking sweat but the thick middle layer has to trap enough heat to keep you warm while letting you swing a rifle or hold a bow.

            While climbing, my middle layer is always a good polyester fleece.  Fleece cannot absorb water and a high quality fleece is lighter than any other material I’ve tried but will still retain more heat than heavier materials such as wool.  Less weight means more mobility and comfort. 

When hunting I’ll switch between fleece pullovers, insulated shirts and wool sweaters depending on how cold the morning is and how much I plan to move around.  One shortcoming I’ve found with fleece is that it’s never wind proof so if there’s a chance you’ll remove your outer layer on a windy day, you’re better off with another fabric.  I especially like insulated shirts because opening the buttons allows a lot of options to cool off as the temperature rises.  Wool shirts work the same way, I just don’t find them as comfortable.

Outer Layer

            Your outer layer is your defense against Mother Nature.  Like your base and mid-layers your outer layer helps trap your body’s heat, but it also has to stop the elements that can attack from outside.  Your outer coat has to withstand the harshest winds while repelling whatever the sky throws at you and still hold your body heat.  That’s the definition of fabrics like Goretex but many other fabrics, including tightly woven wool, offer protection from wind and rain.

            In the beginning I always wore a Goretex coat when climbing but in the past few seasons I switched to a heavy nylon jacket because it was more comfortable.  It works just as well at holding my heat in and the wind out but it’s too noisy for hunting.  My brother and I still argue about what’s the best fabric to climb in but even he has to admit that today there are many fabrics that are windproof, waterproof and warm.  If it’s quiet, too, it will be a good outer layer on stand.

Styling

            Choosing the proper materials for your base, mid and outer layer is not the end of the process.  To maximize heat retention you need to size the layers to optimize air’s insulating qualities.  The tighter your clothes fit the faster heat will transfer from one material to the next and the faster you will cool down, which is why thermal windows don’t touch and why down that lofts the highest keeps you warmest.  If your mid layer fits loosely over your base layer and your outer layer fits loosely over your mid layer, you’ve created two additional pockets of air that heat will have to pass through to get away.

            A few years ago I found this extra space was especially valuable in boots when I was forced to wear a pair a half size too large.  Since that day I’ve only bought hunting boots a half size larger than my dress shoes and my feet have stayed drier and warmer with a thermax liner and a wool sock inside an insulated boot, especially while walking.

            The style of your layers can also help regulate your body’s temperature.  A fleece top with at least a mid-length zipper allows you to vent excess heat while walking to a stand or if the temperature rises with the sun, which minimizes sweating, which also causes heat loss.  Today even base layers have buttons and zippers that let you regulate heat retention and wicking.

            Finally, through climbing and hunting I’ve learned that the reverse of my mother’s favorite winter lecture is true.  She always said to wear a hat because half of your body’s heat escapes through your head.  I have no idea if that figure is accurate, but I have found that removing my hat cools me off quickly.  Because I’m required to wear a blaze hat while walking to my stand I always have a thin baseball one in my pack to trade with the insulated one I wear on stand.  By switching back and forth, I stay legal and comfortable.

            A well planned three layer system keeps you warm and lets you cool off.  Just remember that all of your body feels cold so you may need glove liners to layer under heavy gloves or a balaclava to slip under a thick hat that might fit under a loose hood.  By opening, closing or removing layers you can stay comfortable to hunt harder and stay drier to spread less scent.