For most temps below freezing, good XC ski pants are usually the best, windproof in the front, breathable in the back, it's what most of us use here in Anchorage. As a secondary, tech/softshell type pants can be ok, but often have to be thicker or used with a base layer. Pants like Craft XC ski pants are mind-blowing in the temperature range they are comfortable in. When it gets real cold, like -0 to -20F, I throw on a lightweight shell over everything, like some side-zip waterproof pants. The lack of breathability with those (or anything waterproof) helps trap heat, which you only want to do if it's crazy cold, because the number one problem is usually venting heat and not sweating. I also find it's important in such conditions to be able to change out clothing (using a frame-bag, etc). I tend to bring the "next level" of clothing with me, so a packable puffy real down jacket, those pants, because your body output can affect your heat/moisture situation radically, doing a downhill can super-cool you. So for the most part, we wear what XC skiers do, they have similar output levels and speeds, so similar wind block and breathability requirements.
A forum community dedicated to Mountain Bike owners and enthusiasts. Come join the discussion about bike parts, components, deals, performance, modifications, classifieds, trails, troubleshooting, maintenance, and more!