The Best Thermal Pants

Thermal pants, typically called long johns or long underwear, provide insulation for cold-weather sports like skiing and winter running. A vital part of an active wardrobe, these pants keep you warm, dry and safe when the temperatures dip. Different types of thermal underwear come with their own pros and cons.

  1. Blended Polyester Thermals

    • The most traditional and least expensive way to go, blended polyester, typically polypropylene or a proprietary name, provides all the benefits you need. It wicks moisture, provides base-layer insulation and dries quickly when wet. Synthetics are best for wet conditions -- either from outside precipitation or heavy perspiration -- because they dry the most quickly. Some options include Helly Hansen's Lifa garments and Patagonia's Capilene.

    Merino Wool

    • Merino wool base layers provide a few unique benefits. The natural fibers are both renewable and naturally anti-bacterial. That latter quality means you can wear merino clothing for several days in a row -- like on a week-long ski trip -- without smelling terribly. Instead of wicking moisture like synthetics, merino wool absorbs the moisture away from your body, keeping you dry and warm. While other types of wool can be itchy and uncomfortable, merino is soft and itch-free, especially if it's blended with another fabric. It is generally warmer than synthetics. Companies like Icebreaker and Ibex specialize in merino wool thermals.

    Silk Thermals

    • The minute you touch silk, you know you want to wear it next to your skin. Despite feeling soft and cool against the skin, silk actually provides the best insulation for cold weather. Treated silk pulls moisture off the skin, though not as fast or effectively as synthetics or wool. Companies like REI and Terramar market silk and silk blends.

    Weights

    • It's also a good idea to consider the weight of the garment when choosing base-layer pants. The weight refers to the thickness and warmth factor of the fabric; the weight you choose should be based on the degree of cold, your personal body chemistry (some are naturally warmer than others) and the level of exertion. If you plan to use the pants for high-exertion activities like running or snowshoeing in moderate winter weather, you'll opt for a lightweight fabric. On the other hand, if you're planning for very cold temperatures with low or moderate exertion, you'll want a mid-weight or heavyweight pant. The warmth provided by your mid and outer layers also play into the decision on weight of your base layer.