Arcteryx's warmest first layer, the Kyanite baselayer bottom is made from Polartec® Power Stretch® Pro providing a durable nylon face with a soft brushed fleece backing. These cozy heavyweight layers are for the bitter days or if you rock an uninsulated shell pant. Added warmth that's still easy to move in. It won't be the cold kicking you offhill early if Kyanite has anything to say about it.