Clothing: the COLD rule

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The U.S. Army teaches the COLD rule for dressing in the cold:

Clothing: the COLD rule
Letter	Rule	Why
C (Clean)	Keep your clothing clean	Dirt and grease flatten the fibers and reduce the trapped air, which is what keeps you warm.
O (Overheating)	Avoid overheating	Sweat wets your clothing from the inside. When you stop, that moisture chills you quickly. Take off a layer before you sweat, not after.
L (Loose, Layered)	Loose clothing in layers	Several light layers trap more air than a single thick one, and let you adjust. Tight clothing cuts off circulation to your hands and feet.
D (Dry)	Keep your clothing dry	Wet clothing keeps you warm very little. Change wet socks as soon as you can; shake off the snow before entering the shelter.

The three layers

Base layer (next to the skin): wicks moisture away. Merino wool or synthetic (polyester, polypropylene). No cotton: it absorbs sweat and stays wet.
Middle layer (insulation): traps air. Fleece, wool, a down jacket or one with synthetic fill. Several thin layers are better than one thick one.
Outer layer (protection): blocks wind, rain, and snow. Waterproof or water-repellent jacket and pants, ideally with a hood and with vents.

A hat that covers your ears; a balaclava or scarf to cover your mouth and nose in intense cold.
Mittens over thin gloves: mittens are warmer than gloves.
Wool or synthetic socks, and a spare dry pair in a waterproof bag.
Waterproof boots with room to wiggle your toes.
Sunglasses in snow, to prevent snow blindness.

Figure 14.1. Three-layer system. Adjust by removing or adding layers so you neither sweat nor get chilled. — **Figure 14.1.** Three-layer system. Adjust by removing or adding layers so you neither sweat nor get chilled.

Wind chill

Wind chills the skin much faster than still air. The National Weather Service publishes the wind chill in its forecasts. NWS example: at 0 °F (−18 °C) with a 15 mph (24 km/h) wind, the wind chill is −19 °F (−28 °C), and exposed skin can freeze in 30 minutes. At lower values, in 10 or 5 minutes. Cover all exposed skin when there are extreme cold warnings.