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.
For industrial and military applications it is important to remember that fleece will melt and burns at low temperatures causing serious burns to the wearer. The material can also pack out after prolonged use. This is a terrific material for jackets, pants, mitts, and toques. Because it breathes well and dries quickly it is well suited for active sports. Thinsulate The miracle fabric that almost was.