A raised or strengthened seam that can be used to join many materials, from copper, zinc and lead to textiles. The welt seam is made by folding one side of the material over and under again to enclose the other; stitching or heat pressing keeps the seams together. For textiles the seam lies as flat to the main fabric as possible; in the case of roof joints, the seam is raised above the main surface so that rain runs off it.
* In America, welt describes a gusset or decorative border.