Thats actually a very good question. It can be difficult to find the right pant for wearing under a harnesssomething thats comfortable, wearable in varied weather conditions, and reasonably tough. Ive long preferred tights for this application because they tend not to bind or snag and fit well under a harness. Outdoor Research, I think, used to make a great pair of climbing tights out of a Cordura blend that wore like iron and offered good protection from skinned knees, pokes from sharp rocks, etc. But today its hard to find tights that arent aimed more at cold-weather sports or that have the heft to stand up to climbing.
Most companies now offer pants, and this isnt necessarily a bad thing. Fabrics have improved so much in recent years that pants now have stretch, durability, and multi-climate performance. Outdoor Research, for instance, sells the Exos Pant ($165; outdoorresearch.com), which has some Cordura in the fabric for a very tough pant. They have a lightly brushed interior, so may be too warm when temps are above 50. For warmer weather, Mountain Hardwears Runout Pant ($60; mountainhardwear.com) is made from tough cotton canvas and cut so that a harness wont bind around the waist and your legs have room to move. Patagonias Stretch Jackalope pants ($85; patagonia.com) are made from nylon with a touch of Spandex for stretch, and are specifically designed for climbing, with pockets placed where a harness wont cover them.
Right now, though, I think the supreme climbing pant in all but summer conditions is the Arcteryx Gamma LT (arcteryx.com). These pants have an amazing temperature range in which theyre comfortable (from below freezing to around 60 or higher), and they stretch for comfort, fit great, and are made with Schoeller fabric thats surprisingly tough, given its soft hand. Yeah, theyre $150, which is pretty steep. But once you wear them, all you can say is... Oh!"
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