INSULATING ELEMENT

An insulating element for sealing off a structural element in a motor vehicle, including a carrier and an expandable material that is arranged on the carrier. The insulating element has a top side and a bottom side which, in a state of use, are aligned substantially in a plane of a cross section of the structural element that is to be sealed off. In addition, the insulating element has at least one guide element, by means of which the insulating element can be arranged on a rail element, with the result that the rail element is arranged substantially perpendicularly to the top side and to the bottom side.