What is the Boreas Pull-on, exactly? Is it a long-sleeve shirt? Is it a soft-shell jacket? It's hard to pin it to one particular category, because its performance spans so many. In basic terms, the Boreas is a lightweight stretch pullover made of Matrix SWS (Single Weave Stretch) fabric. The hood makes it look like a cold-weather piece in photos, but it's really at home providing sun protection in warmer climates, whether they are deserts or glaciers. That's what's so interesting about the Boreas you could wear it on the beach in the summer just as easily as on a trek to base camp in the Himalayas.