To make something truly impermeable to water, holes need to be eliminated. This means waterproof garments have to be made in a way that doesn’t involve needle stitching. Seam taping is an exceptionally effective method of making a technical piece of outerwear watertight.
By using strong nylon cloth with a fine but resilient rubber backer, the stitching between the sleeves and the main body can be sealed against water permeation. Taped seams are a key indicator of a heavy duty waterproof garment.