This is a Goodyear-welted product using PVC for the welt. The upper and sole are sewn together, not merely glued, like many footwear constructions. This, together with their Z welt-stitch and heat-sealing process, makes it unique to Dr. Martens. This is the only construction that is stitched on the outside and helps footwear take the shape to the foot. The welt is chain stitched to the upper and insole. The outsole is then sewn to the welt around the edge and then heat sealed. This is the sturdiest and most complex of all constructions.