When you step outdoors, the art of layering becomes your smart-technology thermostat.

When you step outdoors, the art of layering becomes your smart-technology thermostat. This tested strategy lets you regulate comfort by slipping layers on and off as your activity level or the weather changes.

To understand layering your clothing, you need to know the function of each layer:

  1. Base layer (underwear layer): wicks sweat off your skin
  2. Middle layer (insulating layer): retains body heat to protect you from the cold
  3. Outer layer (shell layer): shields you from wind and rain and snow

Even if you don’t wear all three layers at the outset, it’s a good idea to take all layers on every outing: You can peel off layers if things heat up, but you can’t put on layers that you didn’t bring along.

Base Layer: Moisture Management

As the next-to-skin layer, a base layer’s job is moving perspiration away from your skin, aka “wicking.” In cool or cold conditions, wicking long-underwear-style base layers are needed to keep your skin dry. That’s essential because it helps to keep you from becoming chilled or worse—hypothermic.

Base layer materials: You have a wide range of fabric options, including synthetics like polyester and nylon, or natural fibers like merino wool and silk. A lot of people simply go with their personal fabric preference.

Middle Layer: Insulation layer helps you retain the heat that’s radiated by your body.

Middle layer materials: Just as with base layers, you have a broad range of options, both synthetic and natural. In general, thicker (or puffier) equals warmer, though the efficiency of the insulating material is also important. Common middle layer materials: Polyester fleece, wool and wool-blend tops.

Outer Layer: Rain / Snow and Wind Protection

The outer layer (shell layer) protects you from wind, rain, and snow. Virtually all outer layers are treated with a durable water repellent (DWR) finish to make water bead up and roll off the fabric. Your outer shell is an important piece in stormy weather, because if wind and water are allowed to penetrate to inner layers, you can get seriously chilled.

Shells can be lumped into the following categories:

Waterproof/breathable shells: Your most functional choice, this type of shell is your best option for full-on squall conditions.

Water-resistant/breathable shells: These are more suited to drizzly, breezy conditions and high activity levels. They're typically made of tightly woven nylon or polyester fabrics that block light wind and light rain.