Steamboat Springs, Colorado-based Smartwool is best known for its merino socks and base-layers, but its insulation pieces have quickly become a staple in my closet, too. One of my favorites is the Corbet 120 insulated skirt.
Packed with 120 grams of Smartwool's proprietary wool-poly blend fill, this skirt has become a crucial layer for winter hiking and cross-country skiing. I love the functional two-way side zipper, which lets me unzip the skirt from the bottom, for extra mobility, or from the top, so I don't have to take off my boots to add another layer.
During shoulder-season climbing trips, I've even unzipped and spread it on the out on the ground as a cozy blanket for my dog. It's one of the most versatile pieces of gear I own.