FZN stands for Five Zero Nine, not frozen, and that's exactly how you'll feel in the 509 FZN Merino Pant. This base layer pant provides versatile midweight warmth with a high-performance Alpine Merino wool blend that's naturally breathable, fast-drying, and odor-repellent—all without the itch. It's far superior to conventional fabrics and compared to grandpa's wool knickers, it's like upgrading your sled from his 1978 Panther to a PRO-RMK.