WATERPROOF
Waterproof ratings are measured in millimetres, this is how much water a fabric can resists. In testing, water is pushed against the fabric through a tube. When the first drops start to seep through, the height of the water in the tube at that time is measured. For example, if a fabric is rated 10,000 mm (10k), it means it can hold back a 10‑metre‑tall tube of water before it begins to leak.