Outer layers operate as waterproof shells while Middle Layers provide warmth. Additionally, Middle Layers are made with technical materials that work in tandem with your Base Layers and Outer Layers to take advantage of their moisture wicking and breathability. These layers are often made of fleece, knits and polyester. Women's Middle Layers are available in two different weights, Midweight and Heavyweight. Midweight Middle Layers are great for late fall and early spring conditions while Heavyweight Middle Layers are reserved for the coldest conditions of the season or for the more sensitive to cold temperatures. Styles are available in jackets, pullovers and quarter-zips.