The grid fleece pattern collects pockets of warm air to keep us insulated in the cold while also releasing excess heat and moisture when our body temperatures spike during high-exertion activities. The nylon panels in front address fleece's Achilles heel—wind—with an internal windbreaking layer while the integrated thumbholes make it easier to layer under a shell in our cold-weather laying system. * Sierra Designs' best zip-up fleece for everyday * Heavy-weight fleece holds in warm air for insulation * Grid-fleece pattern also facilitates breathability * Stretch fleece and fitted hood keep things streamlined * Internal nylon windbreaker panel in front to cut the wind * Zippered chest and hand pockets to store small items