Without a doubt, the most important part of a waterproof MTB pant is its ability to keep you dry regardless of how frequent the puddle splash is or how heavy the downpour is. Waterproofing is measured by how many vertical millimeters of water are supported by an inch circle of fabric over 24 hours without leaking. The fabric needs to support a minimum of 1,500mm but some fabrics will be rated at 50k plus and, as a rule, the higher the fabric rating the more waterproof the whole product is. But, in the real world, regardless of how good the technology is said to be, no set of pants are totally waterproof and if you’re out for prolonged periods of time in torrential conditions you will get wet. But with the best waterproof MTB pants, it’s just a case of how long this is before the water does begin to seep.