A device for reinforcing and sealing a structural element in a motor vehicle including a reinforcing element which has a longitudinal axis and which is disposable in a cavity of the structural element, wherein the reinforcing element includes walls which extend substantially in the direction of the longitudinal axis, wherein part-regions of the walls on an external circumference of the reinforcing element form at least one strip which encircles the reinforcing element and which runs transversely to the longitudinal axis of the reinforcing element.