3Mâ„¢ Bair Huggerâ„¢ blankets are specially designed to have the perforated side of the blanket on the patient's skin. This ensures optimal heat transfer and clinical warming to the patient. We don't recommend placing any blankets or sheets between the Bair Hugger warming blanket and the patient as this will reduce the effectiveness and may cause uneven heat distribution to the cloth blanket or sheet.