The hardest thing about humanity was the cold. Without the heat of his grace burning and the soul of a vessel to keep him warm, Cas was always in search of a blanket, or sweater, or extra pair of socks.
He would bundle up in layers of fabric and bury himself in afghans on the couch when they settled in to watch Dr. Sexy M.D. every Thursday. Dean would hold his hands in his own larger ones and, when he wasn't too distracted by the drama onscreen, he would rub Cas's skin against his to keep it warm.
Assured that his friend's body would adjust in time, Dean did what he could to make the fallen angel comfortable when he could, even if it meant too many covers on the bed and Cas's cold hands warming up under his shirt when they spooned. Dean would settle into bed with Cas right behind him as the hunter steeled himself against the freezing toes that would inevitably end up warming in his knee pit.