Shell pants are pants with a membrane in the outer fabric that blocks out water and wind, but lets moisture through from the inside. The thing to keep in mind when choosing shell pants is what requirements you have for insulation, durability and weight. 2 and 2.5 layer shell pants are very light and flexible but do not have the same durability and warmth that you get in a 3 layer shell pants. Also think about the number of pockets and their location and if they have zippers on the legs if you want to be able to put on / take them off with the shoes on. If you have any questions about the choice of trousers, please contact us and we will help.