How to Layer Outerwear - (Provided by REI)

Staying comfortable outside is a matter of dressing to outwit Mother Nature. It's a balancing act between the climate, your activity level, exposure time and tolerance to heat and cold. Choosing the right clothing and layering it properly can make the difference between a pleasant outdoor experience and an uncomfortable (or even dangerous) situation.

Layering. The concept applies to any outdoor activity. The trick is to keep your core body temperature consistent no matter what your activity level (vigorous hiking, climbing or enjoying a campfire) or the outside conditions (rain, icy wind or snow).

There are three basic stages in layering: an inner, moisture-management layer, an insulating middle layer and a weatherproof outer layer. You make adjustments depending on the degree of exertion and the outside conditions. The ability to peel off layers as you heat up and add them when you cool off is the key to this system.

More than any other, the moisture-management layer influences how you regulate your body temperature. Have you ever worn a cotton T-shirt under your raincoat while you hiked or walked briskly? Even though you weren't getting wet from rain, you probably felt wet and cold.

Trapped inside your clothing, perspiration can leave you chilled, no matter how well your outer shell fends off rain and snow. Cotton does an effective job of retaining perspiration where it can leave you feeling chilled.

Your next-to-skin layer should be materials other than cotton. Silk, wool and synthetic wicking fabrics such as REI MTS®, Patagonia® Capilene®, Polartec® PowerDry® and CoolMax® polyester work to transport perspiration from the skin. Rather than absorbing moisture, these fabrics disperse it on the outer surface, where it can evaporate. The result: You stay warmer even when you sweat.

Examples: Keeping dry is important for maintaining a cool body temperature in the summer and avoiding hypothermia in the winter. Base layers can be anything from briefs and sports bras to long underwear sets (tops and bottoms) to tights and sport shirts. Thermal underwear is available in light-, mid- and expedition-weights. You can select the right weight to match your activity and the temperature.

Some garments are designed to fit very snugly for better performance, range of motion and easier layering. For hot weather, the wicking layer often consists of a loose fitting, mesh garment.

The insulating layer helps you retain heat by trapping air next to your body. Polyester fleece vests, jackets and tights are good examples of insulation suitable for outdoor activities. They not only trap air but are also made with moisture-wicking fibers.

Insulating layers keep you warm by holding in body heat. Fibers such as wool, polyester fleece and down are all excellent insulators. Wool sweaters and shirts offer reliable warmth and insulate when wet, though they are bulkier than their synthetic cousins.

Polyester fleece such as Polartec® and insulation such as Thinsulate® provide lightweight warmth for a variety of conditions. For extreme cold, dry conditions, goose down can't be beat. It must be kept dry to maintain its insulating ability, however.

Fleece is a favorite insulation material because it's lightweight, breathable and insulates even when wet. Plus, it dries faster and has a higher warmth-to-weight ratio than wool.

Like thermal underwear, fleece garments are available in three weights for different uses:

• Lightweight for aerobic activity or mild climate
• Midweight for moderate activity or climate
• Heavyweight for low activity or cold climate

Examples–For high-energy activities such as Nordic skiing, biking or running, choose lighter-weight fleece to avoid overheating. Tights or tops made of Polartec® 100 (such as REI Teton) or Polartec PowerDry® are excellent for this. For very cold conditions, try thicker fleece such as Polartec® 200 or 300 and those with a wind-blocking membrane, such as Windbloc® and Windhibitor®.

The shell layer protects you from wind, rain or snow. Properly designed, it holds in your body heat while allowing water vapor to escape. If wind or water is allowed to penetrate to the inner layers, you begin to cool off. Without proper ventilation, perspiration can't evaporate. Instead, it condenses on the inside of your shell.

For anything more than light activity, your shell needs to be breathable or well vented to keep perspiration from collecting and chilling your body. The shell layer should also be roomy enough to fit easily over other layers and not restrict your movement.

Examples–Tightly woven fabrics, waterproof coatings or laminated, technical membranes act as wind and water barriers, while features such as vents and zippers add to the garment's overall function. Shells are available in the following constructions:

Waterproof/Breathable–These keep you comfortable in any weather and just about any activity, and are especially suited to wet, cold climates and alpine activities. Fabrics include Gore-Tex® and REI Elements® membrane laminates.

Waterproof/Non-Breathable–Typically made of a durable, polyurethane-coated nylon, which is water- and windproof, these economical shells are ideal for light activity in heavy precipitation.

Water Resistant/Breathable–These are breathable outer layers for mild weather, light precipitation and high activity level. They're made of tightly woven fabrics (such as mini ripstop nylon) that block the wind and treated with a durable water-resistant outer finish to make water bead and roll off.

Some outer shells have a layer of insulation built in, making them suitable for cold conditions, but not as versatile for layering in a variety of temperatures.