An underlay or overlay through which temperature-regulated air is circulated as part of an external circulating-air core temperature regulation system, intended to elevate and/or lower a patient’s core body temperature, typically in surgical and intensive care settings. Air temperature and flow are regulated by a separate control unit (not included). The device is available in a variety of lengths, widths, thicknesses, and shapes to accommodate body size and application (e.g., adult/paediatric, full-/partial-body). This is a single-use device.