A convective blanket may be converted from an underbody blanket to a combination over body and underbody blanket by having an openable seal positioned substantially orthogonal to the longitudinal axis of the blanket away from the head area of the blanket. The seal may be preformed with a line of weakness so that it may readily be separated to form an opening for the head of the patient. The upper portion and the main portion of the blanket may be folded relatively towards each other to cover opposite sides of the patient. Elongate openings are provided in the main portion of the blanket to allow the arms of the patient to extend through the blanket.