A. Waterproof ratings are designed to give an idea of what conditions the garment is suitable for. Waterproof ratings are given to a product after testing. In a hydrostatic head test a section of the fabric is sealed under a tube, water is then filled up to see how much water it can withstand before it begins to penetrate the material. A waterproof rating of 2,000mm means the garment took 2000mm worth of water pressure before it began to leak. The higher the number, the more waterproof something is. The minimum rating for a garment to be waterproof is 1500mm.