To a great extent, our ultra heavy flannel (UHF) shirts define Iron Heart: heavy, rugged, but amazingly wearable. The 12oz fabric is woven with Aspero cotton from the foothills of the Andes mountains. We double brush it on the inside and single brush it on the outside, resulting in a very soft yet substantial, thick, warm and windproof flannel. This shirt is a wardrobe staple - seen here in our work cut in navy with woven wabash-inspired chalk stripes. For FW24, we've upgraded the buttons on this season's flannel work shirts. Instead of the two-hole cat's eye buttons used in previous models, the shirts now feature more robust four-hole buttons for a more secure fastening. Ultra Heavy Flannel Chalk Stripe Work Shirt - Navy