Hypothermia is a condition wherein the core body temperature drops from its “normal” temperature, with normal being between 97.7 and 99.5 degrees Fahrenheit. Some symptoms, in order of increasing seriousness, are cold extremities, mild shivering, mental confusion, muscle incoordination, severe shivering and shaking, combativeness, paradoxical undressing, and cardiac arrest. A drop in core body temperature of as little as three degrees can result in these symptoms and eventually lead to death.
Hypothermia should be a concern with anyone who lives in Western Washington, given our wet, temperate climate. Its prevention, identification, and treatment must be in the forefront of our minds while operating outdoors for periods longer than one hour; it is as important as proper hydration and nutrition. Hypothermia will not only decrease your individual readiness, it will also affect team readiness, as a team member with hypothermia will divert resources from the team’s operational capability. A five-person team can be rendered ineffective, if just one member becomes hypothermic.
This article will explore the prevention, identification, and treatment of hypothermia.
An ounce of prevention is worth a pound of cure. In Western Washington, staying dry is the best preventative. Staying active, fed, and hydrated are close seconds. In order to stay dry while operating outdoors, the proper clothing is essential. If you take nothing else from this article, take this: COTTON IS ROTTEN. Even in the summertime, cotton clothing can lead to hypothermia. Why is that?
Cotton is a hygroscopic fiber; this means it attracts water. Water will be wicked into the fibers to such an extent that a pair of blue jeans will absorb several times its own weight in water. Even without complete immersion, an entire cotton garment can become saturated. That water will then be held against the body. As water conducts heat better than air by several orders of magnitude, a greater amount of body heat will be transferred away from you into the wet garment and from there into the environment much faster than if you were dry. The hygroscopic nature of the fiber will prevent most evaporation from the garment, especially on a humid day.
Two sources of wet clothing exist: external and internal. External moisture is rain, snow, falling in a river, et cetera. Internal moisture is your own sweat. A waterproof outer layer is not sufficient itself; it must be paired with a base layer made of hydrophobic materials– material that does not absorb water– in order to move sweat away from your body and into the environment. Cotton clothing underneath a waterproof outer layer will not keep you dry and warm, even if your outer layer is a breathable water barrier; your sweat will saturate the cotton and keep it next to your body.
Your best defense against hypothermia in Western Washington outdoor operations will be wearing clothing made from wool and/or synthetic fibers. However, as most military field clothing is made from a blend of synthetic fibers (nylon, polyester, polypropylene, and para-aramid) and cotton, that will be the most common textile in use during our group’s field operations. Fortunately, many garments exist made from hydrophobic materials. Any moisture that is absorbed into the fabric is quickly migrated to the environment. Polyester, polypropylene, silk, and wool are examples of hydrophobic fabrics. When garments made from these fabrics are paired with a waterproof outer layer (breathable membrane is the best), you are 90% of the way to preventing hypothermia in Western Washington. Wool is nearly obsolete as an outdoor fabric, except to us old goats who still think man has yet to improve upon nature in that regard.
One can model their field clothing choice based upon the Army’s Extended Cold Weather Clothing System (ECWCS) concept. (The Marines’ equivalent is Mountain/Cold Weather Clothing System.) It consists of a polyester base layer , a polartec fleece mid-layer , and a breathable membrane outer layer . Of course, cost and availability may limit many of us, but we can use the above as a guideline. What follows is my personal advice on what clothing items you should wear in the field.
Anytime the ambient temperature may be below 60 degrees, or there is a good chance of precipitation, one should wear a base layer of thermal underwear , with full length sleeves and legs, that is made from polyester or polypropylene. One can find used thermals inexpensively at surplus stores; I often find complete sets of long sleeve tops and ankle-length bottoms for $10.00. Short sleeve tops  and boxer shorts  can be found for even less. Get the lightweight version first. Medium weight is available, but in my opinion it is too heavy for most applications in our local environment. You will need to experiment with the most comfortable combination, given the outside temp and activity level, but one should own at least one set in each length. Two or more of each set is preferred, so one can change into a clean, dry pair at the end of the day or after falling into a lake.
On your feet should be a pair of socks  made of at least 80% wool with the balance made from synthetic fibers. Having several pair is a must. You may consider a lightweight base layer of a sock made from polypropylene to wear underneath the wool sock. Test out your socks with your boots before going into the field. I have found that I need boots ½ size larger than my shoe size to accommodate medium- to heavy-weight socks. As for the boots, unless it has not rained for several days, rubber boots  are advised for around camp and on patrol, if they are comfortable enough. Leather boots  that are waterproofed with beeswax  and have a breathable, water-proof layer are ideal unless operating in a marshy environment. The Army and Marines now issue boots of a combined leather and nylon upper with a breathable membrane liner.
Anytime the ambient temperature may be below 40 degrees, I recommend adding a mid-weight Polartec™-style fleece, especially if your operations include sedentary activity, such as guard duty or LP/OP duty. One can use civilian versions in multiple colors, but earth tones are recommended for tactical/field operations. I usually do not recommend a mid-weight layer below your waist, unless you will be sedentary in sub-freezing temperature. However, your own experience will be your best guide. The key is to find the balance between too cold and too warm.
If you are sedentary and feel just right comfort-wise, remove a layer before becoming active. For example, if you are on guard duty or radio watch and then go on a patrol, remove your mid-weight layer before starting the patrol. Being slightly chilled at the beginning of a patrol or other activity is fine, because the activity will warm you up. If you have to hike several miles to your LP/OP, put your mid-weight top in your pack to don once you arrive at your destination.
Your outer layer should ideally be a breathable thin shell, such as Gore-Tex™, but cost and availability may limit you. In such case, your outer layer should be wool, or a hydrophic synthetic material such as nylon or polyester. A waterproof poncho  is a less expensive alternative and can keep rain off of you and your gear. Most camouflage clothing can be obtained in a cotton blend with these synthetic fibers, but avoid 100% cotton except for warm dry areas. The cotton blend will still get wet but not as wet as 100% cotton and your base layer will continue to insulate you when wet.
As part of your outdoor ops clothing kit, one should have a fleece cap  and gloves. A cap can be easily donned and doffed, depending on activity level to keep you comfortable. Gloves such as Mechanix ™ or a similar make are made from synthetic, hydrophobic fibers.
A note about the flame-esistant Multicam™ or ACU clothing: Current issue is made from 65% rayon, which is a fiber made from cellulose (wood pulp). Rayon is a hygroscopic fiber like cotton. It breathes very well but will absorb water, like cotton, and even when dry provides minimal insulation. The balance of the blend is para-aramid (Kevlar™) and Nylon added for durability. Like cotton blend garments, it is not as absorbent as a 100% cotton garment, but it’s more absorbent than a 100% synthetic garment.
A further note about Gore-Tex™ and other waterproof, breathable membranes: These breathable membranes work when the relative humidity inside the garment is greater than outside. If the outer layer of the garment becomes saturated, the membrane will no longer be breathable. It will still be waterproof, but your sweat will dampen your clothing from the inside. Breathable membrane garments should not be washed with regular detergent, as the residue will cause water to absorb into the garment rather than bead off. Use Nikwax ™ or similar product for use on breathable membrane garments. For caked on mud or dirt, allow it to dry then brush it off.
Following the above guidelines will help prevent most instances of hypothermia. Of course, it is not a 100% preventative. Should you become wet, it is still highly advisable to change into dry clothing and get something warm to eat and drink by the fire at base camp.