These pants were designed to be my favorite leg layer. Over tights, they keep me happy in a huge range of temperatures, and are comfortable light, and well designed. Cut tighter than cheap fleece pants, they dont have excess fabric flapping around. Each panel has been chosen from a selection of fabrics for the most functional effect. The nicest thing about these pants is the fact that they are fleece along the entire front face of the pants, and around the ankles in the back. However, the backs of the knees through the back waist is made out of lightweight Malden Mills Powerdry fabric- the same as in long johns or polypro tops. This makes sense for a number of reasons. First, when my legs sweat it is mostly around the back of the knees and the ass (gasp!). The lighter weight polypro fabric in these places feels better damp, and keeps the area cooler. It also wicks very well. The ankle to knee on both front and back are lightweight 'checkered' fleece- the stuff that has the grooves in it for less weight and more dead air space. I kept the fleece in the back of the ankles because in frigid weather I can't afford for my feet to get cold, and I need to keep the arteries feeding the feet warm blood. The front knees are 200 weight powerstretch, articulated, and the front thighs and waist are 100 weight fleece. Side zips run from the ankle to a few inches below the waist. This is nicer than full size zips because the leg openings are amply big enough to fit over the biggest plastic boots (including my clunky size 11 invernos, and they fit easily). Not having a full separating zipper means that there are two less tiny zipper pulls to fumble with in subzero temperatures, but with the functionality of side zips where you don't have to shed boots to change layers. It also helps not to have to zipper pulls under your pack hip belt, assuming you have one on your size zip shell pants.