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So, you're in the market for a new rain jacket (or ski shell and pants or any other waterproof breathable apparel). And you see in the tech specs listed or on the garment hangtag a number (such as 5K or 10,000mm) that's supposed to give you an idea of how waterproof that garment is. And maybe you think, But that makes no sense—isn't waterproof an absolute term? Something is either waterproof or it isn't, right? Or, maybe you think, 10,000mm? WTF does that mean? Yeah, we understand where you're coming from. The term "waterproof" should mean, literally, something that is impervious to water. That’s what it used to mean before the advent of waterproof breathable materials. Metals, glass, and thick rubber are waterproof. Waterproof breathable fabrics, however, are highly, highly water-resistant. And it's in this realm of “waterproof breathable” materials that testing and rating and confusion begin.


Tests of waterproof materials generally measure two criteria:

• rain-room endurance
• static column water resistance

Manufacturers tout “rain rooms” as research tools, but rain-room testing is conducted primarily to meet International Customs requirements so fabrics can be classified as waterproof or not and receive the correct import duty. Rain-room testing is not generally a good measure of a fabric’s capabilities. Static-column testing is designed to measure a material’s absolute water resistance, using a standard millimeter (or pounds-per-square-inch conversion) measurement. In static-column tests, a 1-inch diameter tube stands vertically over a piece of waterproof material; the tube is filled with water, and the measurement is the height of the water column in millimeters when leakage begins. When published, the ratings appear as "20K mm" or "20,000mm waterproof." Most companies producing waterproof materials use a variation of this test, and the results are made available for comparison and marketing. The results are accurate (to a point), which is great, but in terms of "real world" testing, they aren’t very applicable. Where the various materials measure up is a topic for another time, and it is a major point of contention. Nobody seems to be able to produce accurate, controlled test results for every waterproof breathable material. We've tried to create a scale that shows the "real world" translation of mm waterproof measurements, but keep in mind that companies employ multiple variables that affect test results, whether intentionally or unintentionally.

WATERPROOFING IN MM TRANSLATED

• 0mm: obviously not waterproof in any way. Sieves, screen doors, basketball nets.
• 0mm-1000mm: rain resistant, but not rainproof. Most stretch-woven softshells fall here.
• 1000mm-5000mm: rainproof but not waterproof under pressure (sitting on or leaning against wet surfaces). Engineered (laminated) softshells, inexpensive rain shells, low-end ski and snowboard wear.
• 5000mm-15,000mm: totally rainproof and generally waterproof unless under serious pressure (extended sitting, submersion, heavy people sitting). Most proprietary coatings (generally, liquid polyurethane coatings that become porous when applied to fabrics and cured) fall in this range.
• 15,000mm-30,000mm: totally waterproof, even under serious pressure. High-end proprietary PU laminates, PTFE membranes like eVent and GORE-TEX® fabrics. Can withstand shallow-depth submersion without leaking (fishing waders, drysuits for sailing).
• 35,000mm and up: Solid vessels and non-porous materials. Will deform or fail catastrophically before leaking. Nalgene bottles, rubber galoshes, aircraft carriers.

Patagonia Rain Shadow Jacket; photo, Greg Coffin, community member
Unfortunately, though this all seems straightforward, it’s not. Most companies test waterproof materials by themselves, while only a few test after application to fabric. Other variations abound; Helly Hansen, for instance, maintains that it is one of the only companies to test every garment after five wash cycles. That sounds burly, but when you change the testing conditions, you lose any realistic or direct comparison with other companies. Gore, on the other hand, goes in the other direction by refusing to release test numbers and relying totally on their guarantee of waterproof breathability. Even though a guarantee is nice, it makes comparison just as hard. And remember: this is just the fabric. Not the garment itself. A garment constructed from 10,000mm-capable fabric is not necessarily 10,000mm waterproof. The fabric, often just the membrane/laminate on the fabric, is the only thing that was measured. Seam taping is the next factor, and a huge one. Though a garment’s fabric may be rated to 20,000mm, most seam taping is rated much lower, around 3,000-5,000mm. This occurs as a result of the PU adhesive, which can allow seepage due to imperfect application and curing. On the outside, seams also collect water, causing wet-out and increased pressure. "Critical" seam taping protects only those seams that a company deems important (usually in the shoulders, chest, and sleeves for jackets; lower legs and ass for pants) leaving some seams unprotected. Only fully taped garments are fully "waterproof" under the new definition.