Fleece fabric traps a barrier of air warmed by your own body temperature next to your skin. This means that cold air is trapped outside of the material and warm air is trapped inside, and this is how anti-pill fleece helps your body stay warm. While fleece is trapping warmth close to your skin, its fibers are wicking moisture away from your skin and transferring it to the outside by a process called capillary action. That's how fleece fabric continues to provide warmth even when it's wet.
Fleece is perfect for creating clothing like sweatpants, joggers, pajamas, pullovers and hoodies. Apparel made with fleece is often sought after as much for it's trendy aesthetic appeal as it is for warmth.