Patients assigned to passive insulation will be covered as usual with a cotton gown and single layer of cloth surgical draping. Patients assigned to forced-air warming will also be covered with a gown and surgical drapes, but a forced-air cover (Bair hugger 63500, 3M) will be inserted between the gown and the skin surface. A lower-body cover (about 91 by 221 cm) will be positioned so the lower end of the forced-air segments extend from the ankles upward for the entire length of the cover in thoracic and abdominal cases. The cover's foot drape will extend over the feet, and in turn be covered by the surgical drape. An upper-body forced-air cover will similarly be applied for patients having hip arthroplasties. The forced-air cover will be connected to a Bair Hugger blower and #635 covers set to "high" (≈43°C).