If you truly want to keep the rain off your legs and stay dry and warm, a pair of hardshell trousers is a must. But there's more to it than simply keeping the rain off: breathability is key. Otherwise, your legs will be just as wet – from the inside. Such trousers can be incredibly useful for high alpine mountaineering where you have to contend with deep snow and volatile weather. Look for a good fit, durability, and useful extra features like waterproof pockets, knee/buttock reinforcements, adjustable seams, and ventilation zips.