For non high intensity activities in extreme cold such as down hill skiing, camping, resting, etc. This wonderful material is responsible for a minor revolution in outdoor clothing. Fifteen years ago only Helly Hansen pile was readily available. It was ugly, and fairly expensive, but very good. Today the explosion of colors and various weaves has made this one of the most popular insulators today.
Fleece has the same insulation as wool at half the weight.
It is much more comfortable, and dries very quickly. Fleece is easily washed, an survives years of use and abuse. Unfortunately fleece does have its problems. It doesn't compress well. Wind blows right through the fabric.