Fleece has air which gives it a warm limit that can ingest up to half of its weight. It can sit on the skin without making any aggravations, and rankles fibre empty fibre, so it doesn't retain dampness but instead drives water away from itself and toward the fibre, and that implies there isn't an immersion point. For instance, James can wear his alpaca socks in rain boots (no ventilation) and sweat in the socks and beyond the socks will be soggy, however, his feet will be dry.