A heat-shrinkable envelope is composed of at least one shrinkable planar layer on which a reinforcing component of fiber-shaped or thread-shaped reinforcing elements is arranged. These reinforcing elements are arranged in unregulated configuration, for example in the form of a fleece, felt or in an irregular fill. Advantageously, a cover layer may be applied so as to sandwich and bond the reinforcing component between the cover layer and the planar layer.