Arc'teryx Cerium Vest - Black - Size M I purchased this but have only tried it on and haven't used it. This is a rare item, as it's not widely available each year. A lightweight and warm down vest. It's perfect as an alpine mid-layer, and also works well on its own in cool weather. The lightweight and highly insulating Cerium Vest is the perfect insulation for those who want to minimize their luggage in the backcountry. It doesn't take up much space in a backpack, and can be used as a mid-layer in cold, dry conditions, or on its own to quickly warm your core during breaks at camp. In addition to 850-fill, ethically sourced down, Coreloft synthetic insulation is placed in areas prone to moisture. This achieves high-quality insulation performance. The bio-sourced liner reduces the use of petroleum. The 15-denier Arato™ nylon outer fabric made from recycled materials is lightweight and highly durable. Comes with a stuff sack for compact portability.