Filson's Jac-Shirt is an outdoor staple that provides the versatile warmth that only 100% wool can. The fabric is crafted with a tight weave that delivers an optimum balance of breathability and wind resistance while providing durability for decades of service. Wool’s unique structure makes it naturally water-resistant, moisture-wicking and warm even if it gets wet. It also allows wool to release dirt and odors, making care and maintenance an easy matter. For decades, mankind has tried to manufacture fabrics mimicking wool’s performance. The resulting fleeces and soft shells can perform specific functions quite well, but none can provide the all-around performance of nature’s original miracle-fiber.