The Women's Helix Vest is the sleeveless option in Icebreaker's MerinoLoft line of merino wool insulating layers. With its low bulk merino wool, slim fit, and stretch fabric, the helix layers easily under a shell on cold ski days. The 100% recycled polyester and DWR treated shell fabric makes it equally proficient on its own on cold weather hikes. Merino wool provides several benefits when utilized as an insulation. As you'd expect with any wool garment, it's highly breathable, excellent at retaining body heat, and, with it's low bulk feel, it's comfortable as a mid layer.