The waterproof rating of a fabric is expressed in Schmerbers. You will often find this rating information on the label of your garment. The higher the number, the more waterproof the fabric of your product. So, if you read 10,000 mm or 10,000 Schmerber, the fabric of your trousers can withstand a column of water 10 m high. But to get a perfectly waterproof product, Schmerbers are not enough. The seams must also be made waterproof. Indeed, even if your fabric is water resistant, water can get in through the seams. If you take a waterproof, unlined jacket, for example, and turn it over to look at the inside, you'll see that the seams are covered by a waterproof tape to prevent water from getting inside the jacket.