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What To Look For
You should feel solid about the type of mountaineering boots you wear on a trip or expedition. The right pair of mountaineering boots is different for everyone, but they should perform well, regardless of their style and design. Look for a pair of mountaineering boots that are going to keep you warm and dry, give you proper ankle and load bearing support, and are crampon compatible and climbing friendly if you intend to do any ice climbing. There are leather mountaineering boots and there are plastic ones. Some have a removable liner and others don't. If your feet tend to get cold then you may want to consider plastic mountaineering boots with removable liners. The plastic lets no moisture in and the liners can be kept in your sleeping bag at night so they don't freeze. There are many leather mountaineering boots that will keep you warm too, but it all depends on if you plan on traveling through wet snow and how cold you normally get. Some people prefer leather mountaineering boots such as the La Sportiva Nepal EVO GTX for day trips and plastic ones such as the Koflach Degre for expeditions. Features such as locking laces and removable tongue inserts are nice to have.
Common Pitfalls
Try on mountaineering boots with the types of socks you intend to wear them with. Don't try them on with your thin running socks if you intend to wear them with thick hiking socks, for example. Be aware that many leading brands of mountaineering boots run in European sizes. If you are buying a used pair of mountaineering boots, inspect the soles to see how much wear they have been through. Plastic mountaineering boots last a long time; all you may need to do is replace the laces, but if the soles are pretty worn down you may want to pass. Check to make sure the crampon grooves are still in shipshape. Also, if you intend to use your mountaineering boots for a lot of vertical ice climbing make sure that they have a very stiff sole and good ankle support.
Where To Buy
A good selection of mountaineering boots are usually found at your locally owned gear shops, which also have a good selection of rock and ice climbing gear. If you are determined to shop from home, sites such as Trails.com, Backcountry.com, Altrec.com and Mountaingear.com have a good selection. Used boots can often be found at Geartrade.com or eBay.com. If you live in a mountain town, then local gear swaps or gear sales are also a good place to look for used mountaineering boots. Trying them on first is recommended.
Cost
Plastic mountaineering boots run from $140 to $450 new, but you can find some used pairs for a bit less. Leather mountaineering boots cost $200 to $520. Buying a model from a previous year is always a bit less expensive.