A warm, breathable, fully lined Mackinaw Wool jac-shirt with a snap-closure front. Filson heavyweight Mackinaw Jac-Shirt uses the same 100% virgin Mackinaw Wool that's found on many of our jackets. It's breathable, warm and naturally rain-repellent. A flannel lining in the body provides the softness of a shirt while adding even more insulation. The button front is easy to use while wearing gloves, and a pleated back allows a full range of motion.