When shopping for winter hiking pants, consider buying different layers of pants with different qualities or special winter pants combining the three different layers. The base-layer pants should be made of lightweight material that breathes and does not retain moisture. Treated wool and synthetic material are often used. The second layer is for insulation and should be lightweight and retain air between you and the outside. Waterproof and lightweight nylon is often used. Depending on how cold the environment is, these two layers may be enough. For extreme cold, look for ski or mountaineering pants that combine a very warm under layer with thick insulation.
Be careful not to under-dress for the weather. Hypothermia is a danger if you are out hiking for a long period in cold weather. If you think mountaineering pants are overdoing it, you could buy three layers of pants instead of two. This way you can shed layers if it gets warmer during the day.
Where to Buy
Look for winter hiking pants at sporting goods and gear stores such as The North Face, Backcountry, REI and Altrec. The website hikingandbackpacking maintains an updated list of the best websites for buying hiking and camping equipment from trusted manufacturers. You can use the list to compare stores in different locations for the lowest prices for hiking pants and other equipment.
The first layer is generally inexpensive, costing $10 to 30. The outer layer pants can run from $30 to $100. Ski or mountaineering pants can be especially expensive, costing $100 to $200.
Hiking and camping stores also sell fall and winter hiking coats, sweaters and other cold weather gear made from similar materials as hiking pants. These are also good clothing items to invest in if you don't already have warm clothing for your upper body.