A mid-layer shirt is a versatile piece of clothing that can be used year-round under your shell jacket for a variety of activities. Wool and fleece are ideal materials for a mid-layer. This is because wool has good thermal insulation properties while allowing the body to breathe and regulate temperature. Fleece does not have its own heat capacity but has a porous construction that traps air and keeps you warm. Here you will find functional and durable wool and fleece shirts from well-known brands such as Norrøna, Fjällräven, and Haglöfs.