An impact guard beam for vehicles comprises a beam (11) with a hat profile, i.e., with a crown (13-15) and side flanges (16-17), and the hat profile has its crown facing outwards. The beam has a cover (20) giving at least a central part of the beam a closed cross section. The cover has a profile allowing it to lengthen by straightening out when the hat beam's profile opens under impact loads, but stops the hat beam profile's opening when the cover is straightened out. The cover may carry a sensor (24) for an airbag, which is then placed inside the beam profile.