A non-sterile underlay, overlay, or wrap(s) through which temperature-regulated fluid is circulated with the intention to heat and alternatively cool a patient’s whole-body (i.e., elevate or lower core body temperature) as part of a circulating-fluid whole-body heating/cooling system typically used in the operating room (OR), intensive care unit (ICU), or a recovery unit. The underlay/overlay is available in a variety of lengths, widths, and thicknesses to accommodate body size and application (e.g., adult/paediatric, full-/partial-body). It is intended to be used by a healthcare professional in a clinical setting. This is a single-use device.