A sewing thread has at least on its outer surface at least one precursor of a product which confers to a stitched seam produced with such a thread an increased adherence to sewn materials. In addition, a sewing thread is disclosed in which the applied precursor changes into a product which is capable of increasing the outer diameter of the sewing thread, in particular in an aqueous environment. Finally, a process is disclosed for producing water-tight stitched seams. As indicated in the examples, the precursor is an expandable plastic or can contain inorganic expansion materials such as expanded pearlite, expanded mica or expanded graphite.