The Sinclair Insulated Flannel has all the trappings of a regular ol’ flannel button-up, but it has a secret weapon you can barely notice from the outside: It’s stuffed with 40 grams of Spaceloft™ synthetic down insulation for added warmth. Tough poplin fabric on the forearms helps with abrasion resistance and a smooth taffeta lining on the inside and quick metal snap buttons make the Sinclair easy to take on and off.