|Waterproof Rating (mm)||Resistance provided||What it can withstand|
|0-5,000 mm||No resistance to some resistance to moisture||Light rain, dry snow, no pressure|
|6,000-10,000 mm||Rainproof and waterproof under light pressure||Light rain, average snow, light pressure|
|11,000-15,000 mm||Rainproof and waterproof except under high pressure||Moderate rain, average snow, light pressure|
|16,000-20,000 mm||Rainproof and waterproof under high pressure||Heavy rain, wet snow, some pressure|
|20,000 mm+||Rainproof and waterproof under very high pressure||Heavy rain, wet snow, high pressure|
10,000/10,000? 20,000/20,000? What do the rating numbers actually mean?
Why isn’t outerwear completely waterproof?
How do they do it?
|GORE-TEX® 3 Layer fabric construction||GORE-TEX® 2 Layer fabric construction||GORE-TEX® 2 Layer insulated fabric construction|
How waterproof a garment do I need?
Remember that while a 20,000 mm rating may sound impressive, a hard day of riding in wet conditions with the added pressure of wind, sitting, and falling puts even the most waterproof fabrics to the test.
How are waterproof ratings determined?
Waterproof ratings are determined by the clothing manufacturer or fabric producer, with testing done either by independent laboratories or in-house. There are a number of different testing protocols in use, but most involve the equivalent of placing a 1” x 1” square tube over the fabric and determining how high (in millimeters) a column of water you can suspend over it before it starts to leak. Some manufacturers have developed their own testing methods that involve adding pressure to the process to simulate the effects of wind.
While waterproof ratings are becoming more standardized, remember that different labs may test or report differently, and may come up with different results even with two pieces of fabric from the exact same roll, so take the numbers with a grain of salt. Keep in mind that some manufacturers report waterproof ratings in PSI (Pounds per Square Inch) rather than millimeters, which has a conversion rate of 704 mm = 1 PSI.
How breathable a garment do I need?
If all your riding is lift-served, you don’t hike to out-of-the-way lines, and you take regular breaks in the lodge where you remove your coat, a breathability rating of 5,000 to 8,000 grams will probably be fine. If you do a lot of “high energy” riding or active sidecountry where you often break a sweat getting to your destination or returning to the ski area, look for breathability in the 10,000 to 15,000 gram range. Backcountry hardcores and people who commonly skin or boot for thousands of vertical feet in a day should look for garments with breathability in the 20,000 plus range.
How are breathability ratings determined?
Results can vary wildly based on test, temperature, humidity and pressure and are not standardized from brand to brand, or test to test. Most testing doesn’t reflect real world winter conditions, like near freezing outside temperatures with high relative humidity. Since manufacturers seldom reveal the actual test used, and are probably keen on reporting the highest possible figures to promote sales, it’s best to read these numbers with the eye of a skeptic, but generally within a given brand or family of fabrics it’s safe to say more grams is more breathable (if a company grades breathability on an RET scale – Resistance to Evaporative Heat Transfer – a lower value is better).
Membrane or Coating?
Coated fabrics tend to be very waterproof but lack breathability in comparison to membrane laminates. These fabrics are less expensive and are improving as manufacturers finds ways to make the coatings thinner and more porous. Coated fabrics are great for emergency weather protection or for activities that don't involve a high level of exertion.
What is seam sealing and why is it important?
Seam sealing, sometimes referred to as seam taping, covers the tiny holes made by the needle in the sewing process so they don’t leak, using a heat application of thin waterproof tape. Sometimes seams are bonded together using glue or heat, but typically they are first sewn then taped. Garments can be either “fully taped” or “critically taped” – the difference is that a fully taped garment has every seam taped, while a critically taped one has tape only on high exposure areas like the neck, shoulders, and chest. Without adequate seam sealing you’ll get wet even with the best waterproof/breathable fabric.
DWR stands for Durable Water Repellent. Almost all outerwear exterior fabrics are treated with some sort of DWR. It’s meant to keep the fabric from becoming saturated with water and adding weight. DWR causes water to bead-up and roll off the fabric and is affected by abrasion, dirt and body oils. This is why after some use, a garment will appear to no longer be waterproof. This isn’t the case, though - it likely means the DWR needs to be refreshed by simply washing the garmet (follow the manufacturer instructions). The factory DWR treatment will eventually wear off, too. Aftermarket DWR sprays are available from companies like Nikwax to re-condition your waterproof/breathable garment after washing – try one of these if you notice water soaking into the face fabric of your Waterproof/Breathable garments and you have already attempted to refresh the DWR by cleaning your outerwear.
Nikwax Tx Direct Spray
DWR sprays are best applied to a damp garment after washing and thoroughly rinsing it (do a second rinse cycle without soap before you apply the DWR to make sure no detergent residue remains) and should be heat activated using a medium dryer or iron before use. Read the directions on both your garment and the DWR bottle before you start. Spray DWR applications are easier to use and less time consuming, while wash-in products will reach every nook and cranny of your garment, ensuring you do not miss any part.
What is GORE-TEX®?
GORE-TEX® fabrics are created by laminating a GORE-TEX® membrane to high performance nylon and polyester face fabrics. They come in several different grades, including GORE-TEX® Pro, GORE-TEX® Active, and just regular GORE-TEX®. GORE also offers soft shell fabric and a super light 2.5L fabric called Paclite®. GORE-TEX® garments are fully seam sealed and feature a “GUARANTEED TO KEEP YOU DRY®” promise. Although many laminates are waterproof, a GORE-TEX® membrane is capable of maintaining an extremely high level of waterproofness while staying very breathable thanks to billions of microscopic pores that let water vapor out and prevent liquid water from entering. Introduced in 2013, GORE-TEX® Pro fabrics utilize a new membrane with no Polyurethane protective layer and significantly improved breathability. In 2015, GORE introduced a new backer technology for 3 layer GORE-TEX® fabrics called C-KNIT™ which uses a very fine nylon backer with a circular weave. C-KNIT™ fabrics also have improved breathability, a softer hand, and slide over mid layers more easily.
While some people refer to all waterproof/breathable fabrics as “GORE-TEX®,” it’s a proprietary product and technology of the W. L. Gore Corporation.
The W. L. Gore Corporation is zealous about upholding the reputation and performance standards of GORE-TEX® outerwear, and maintains a strict set of rules for any company making a GORE-TEX® garment. You don’t just buy their fabric and send it off to China for production. They require waterproof, breathability and durability testing of every garment in both design and manufacturing stages, mandate use of GORE seam tape and taping machines, and insist on current factory certification for any facility building GORE-TEX® jackets, pants, gloves or shoes. Serious business.
Electron microscope photography of GORE-TEX® membrane
GORE-TEX® Pro comparison, with the old version on the left and new on the right. Red is face fabric, gray/white is the ePTFE
membrane, and gray strands are the lining. The white PU layer on the left has been replaced by the thin gray ePTFE "sandwich"
in the new version on the right.
WINDSTOPPER® is a different, non-waterproof membrane also manufactured by the W. L. Gore Corporation that blocks wind and is highly breathable. It is usually laminated to fleece or softshell fabrics and suitable for strenuous outdoor activities in clear weather.