The present invention features a removable liner for headgear. The inventive liner is specifically configured for placement within a cap member, hat, or any sort of headwear for enhanced thermal comfort. The liner is comprised of two shell layers that are made from choice performance materials. The two constituent shells are formed together to provide localized climate control for the head of the wearer. A first inner shell, adapted for contact with the wearer, is an ultrathin, thermally reflective, synthetic, microfibrous fabric. This inner shell removes moisture and allows airflow (for heat and perspiration removal. The second, outer shell is a multi-membrane fabric, forms an insulative, breathable, windproof, waterproof layer that lies between the headgear and the first inner shell.