A. All waterproof garments will be given a waterproof rating that is determined with a hydrostatic head test- most often this is expressed in mm. The higher the rating the more waterproof it is. If a garment is 2,000mm waterproof this means the fabric can withstand 2,000mm of water over a day before water will start to penetrate through. The minimum standard for a jacket to be waterproof is 1,500mm so a jacket with a waterproof rating of 2,000mm would be suitable for moderate rain.
See our Waterproof Jacket Guide for more details.