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.