When we talk about waterproof products, it’s not just about the fabric. A lot of it is about the construction and design. When building a product you’ve got lots of separate panels that you sew together. When you’re sewing two panels of fabric together, you’re punching holes in the fabric with a needle and thread. We use seam tape to seal those holes. It’s basically a tape applied to the back of the product through heat and pressure. I would say a waterproof product should have taped seams. It’s specified in a lot of running race’s kit lists because a product is not really classified as waterproof unless it has taped seams.