An underbody blanket, comprising: an air impermeable upper sheet and an air impermeable lower sheet bonded to each other at their respective peripheries to form an inflatable structure having a periphery defining therewithin a head portion, a body portion and a foot portion, at least one inlet port (44a, 44b) provided at the structure; and apertures (26, 28, 30) formed in the upper sheet to enable heated air input via the inlet port to inflate the structure to escape, respective rows of apertures provided proximately along each longitudinal side of a non-inflatable body area positioned to face the patient when the structure is inflated so that the heated air output from those respective rows of apertures is directed to the patient; characterised in that both longitudinal sides of each of the head and foot portions narrowing at a tapered manner toward each other from opposite sides of the body portion to respective head and foot ends (10a, 14a) of the structure so that each of the head and foot portions has the shape of an isosceles trapezoid to facilitate the flow of air inside the structure; the blanket has two elongate openings (18a, 18b) each having a given width and a given length formed by a corresponding non-ending seal (20a, 20b) that encircles the each opening, each non-ending seal having a length extending longitudinally along substantially the length of the body portion, the elongate openings sandwiching the non-inflatable area of the body portion whereon the body of a patient rests when the patient is positioned onto the upper sheet of the blanket; and each of the respective rows of apertures is positioned between the non-inflatable body area and a corresponding one of the elongate openings (18a, 18b). an air impermeable upper sheet and an air impermeable lower sheet bonded to each other at their respective peripheries to form an inflatable structure having a periphery defining therewithin a head portion, a body portion and a foot portion, at least one inlet port (44a, 44b) provided at the structure; and apertures (26, 28, 30) formed in the upper sheet to enable heated air input via the inlet port to inflate the structure to escape, respective rows of apertures provided proximately along each longitudinal side of a non-inflatable body area positioned to face the patient when the structure is inflated so that the heated air output from those respective rows of apertures is directed to the patient; characterised in that both longitudinal sides of each of the head and foot portions narrowing at a tapered manner toward each other from opposite sides of the body portion to respective head and foot ends (10a, 14a) of the structure so that each of the head and foot portions has the shape of an isosceles trapezoid to facilitate the flow of air inside the structure; the blanket has two elongate openings (18a, 18b) each having a given width and a given length formed by a corresponding non-ending seal (20a, 20b) that encircles the each opening, each non-ending seal having a length extending longitudinally along substantially the length of the body portion, the elongate openings sandwiching the non-inflatable area of the body portion whereon the body of a patient rests when the patient is positioned onto the upper sheet of the blanket; and each of the respective rows of apertures is positioned between the non-inflatable body area and a corresponding one of the elongate openings (18a, 18b).