Abstract: Inflatable drag reduction device (20, 22) for vehicles, comprising an inflatable bag of a durable, flexible and generally air-tight material, arranged for attachment to the vehicle. The bag comprises of a plurality of conjoined panels and an air duct arranged for allowing the inflow of air into the interior of the bag when the vehicle is in motion. The bag further comprises internal ribs of a generally non-elastic material attached to the internal surfaces of the panels, that assist the bag in assuming a predetermined geometrical shape in which the panels are prevented from billowing outward.