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Q: What's the deal with these waterproof ratings? What's the difference between a 5K and 20K waterproof ski/snowboard jacket?

Dan
Pittsburgh, PA

A: Dan,

Before I get to the difference between a 5K jacket and a 20K jacket, I need to clarify a few things. A 20K rating, sometimes written as 20,000mm, means that a jacket's fabric can withstand 20,000 millimeters (almost 66 feet) of rain in 24 hours before its wearer gets wet. So, a 5K jacket can take up to 16 feet of rain in 24 hours. Given that the record for the most rainfall in a day is about 6 feet, both options sound pretty damn waterproof.

You should also know that a jacket's waterproof rating is for the fabric, not the entire jacket. A jacket's fabric might be able to handle several feet of rainfall, but if the seams aren't sealed, then water can usually get in. So if you want the best waterproofing, look for a fully seam-sealed jacket (also called fully taped). A 20K waterproof jacket is virtually pointless if the seams aren't taped.

Now, to get down to your question. As I said, a 5K jacket's fabric can withstand 16 feet of rain, but manufacturers generally don't tape all the seams (if at all). These jackets often have a waterproof coating (DWR or Teflon, for example) instead of a waterproof membrane integrated into the fabric (like The North Face's HyVent). Zippers aren't waterproofed. If it dumps snow, you probably won't stay dry very long. The 5K jacket is typically a lifestyle piece or a jacket to wear on sunny days—not one I'd rely on for waterproof protection in the backcountry or a crappy weather day on the ski slopes.

Then there's 10K. 10K is more than 5K, you say? Bingo. You can confidently take that jacket out on a powder day in Utah or Colorado or wear it during a short cloudburst. But it might not hold up to wetter coastal snow or hours in the rain on the Olympic Peninsula. Do take note of its construction—for example, are its seams taped? Does it have waterproof zippers? Does it have a membrane construction?

A 20K jacket will keep you dry in nearly any condition. A manufacturer that bothers to make a jacket from 20K-rated fabric with a membrane is probably going to cover every seam and use waterproof zippers and storm flaps. I would feel confident in any coastal snowstorm in a 20K jacket.

For a jacket that is guaranteed waterproof (and breathable), go with Gore-Tex. A jacket with this fabric must meet very specific requirements from Gore-Tex. It will keep you dry no matter what.