Q. I'm trying to figure out what kinds of clothes I'm going to need for an upcoming winter trip. Friends are telling me to use "layers". What kind?

A. Clothing keeps you warm by trapping "dead" (non-circulating) air and holding it in next to your body. Your body heats this dead air and it forms an insulating barrier between you and cold air, winds and cold surfaces.

The easiest way to stay warm and comfortable in changing temperatures is to dress in a number of light- to mid-weight layers. Layered clothing systems are versatile (you can add or remove different layers in response to changes in the weather or your own internal temperature) and efficient (a number of thin layers is warmer in the long run that one or two thick layers, and they take up less room in your backpack).

To layer successfully, you must consider three different types of clothing layers--underwear, insulation and outerwear. Each type of clothing performs a different task. REI offers lots of choices within each layering category. <br>

Underwear (or inner layers): Inner layers go right next to your skin. Their primary job is to move moisture away from your skin to keep you dry, warm and comfortable. REI M.T.S. 2 Thermal Wear is our best value in thermal undergarments. We offer it in different weights for different temperatures and different activities. M.T.S. 2 comes in sizes for men, women and children.

Insulating layers: Insulating garments provide warmth by capturing and holding the heat that your body generates. The most popular insulation layer today is probably polyester fleece Polartec, for example, which is light, breathable, quick-drying and insulates even when wet. Fleece vests, anoraks, jackets and pants come in varying thicknesses (weights) for varying activities. Fleece can also be worn as an outer layer in mild conditions.

Outerwear layers: The outer layer of a clothing system must protect the inner layers from wind, rain and other weather threats. But they have to be comfortable, too! Outer layers should seal up tight against the elements, yet open freely when a little extra ventilation is needed. Important features like vents, cuffs, hoods and zippers all affect an outer layer's waterproofness and its breathability. The more active you are, the more you'll appreciate underarm zips and other features that keep you well ventilated.

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Send Comments, Questions or Suggestions: Last Modified: December 26, 2006