If you can have just one mid layer in your kit, the Women's Bungy Jacket is quite possibly the one to choose. Haglöfs' durable and stretchy mid layer is made from light Polartec Power Stretch Pro fabric for excellent wicking, warmth and comfort.
Polartec Power Stretch Pro provides an excellent warmth-to-weight ratio with enhanced wicking capabilities, high stretch for maximum freedom of movement, as well as excellent next-to-skin comfort and a smooth outer face for layering. Articulated sleeves help to improve movement further. To avoid chafing and enhance durability, the top is constructed without seams at the shoulders, and with flatlock seams in other key areas. Two mid-mounted zipped pockets keep your essential items at hand.