What Waterproof Gear Ratings Mean
Ever wondered what those labels “5K waterproof rating” or “20,000mm waterproof coating” mean?
It turns out that even Gore Tex and similar waterproof membranes can soak through eventually. Those fabrics are typically rated to 20,000mm (or 20K, it’s the same thing). That means they can withstand at least 20,000 millimeters (about 66 feet) of rain over 24 hours. I did say “at least”, but a few hours under a high pressure hose could eventually soak through even the best membranes. The 5K or 5,000mm ratings mean the fabric can withstand 16-17 feet of rain over 24 hours.
Thanks to Backcountry Bob over at Backcountry.com for the explanation. Check out Bob’s article “What’s the deal with these waterproof ratings?” for a more detailed description than I wrote.