Sledding and snow biking is hard work. No matter how cold it gets; you’re going to sweat under all that gear. That’s where the 509 FZN LVL 1 Shirt comes in. Our lightest weight and fastest drying base layer, it goes beyond grandpa’s long johns to quickly wick sweat. It’s part of 509’s Active Layering System™ featuring Cold Armor™ technology that, when paired with 509 outerwear, creates the ultimate defense against the harshest conditions.