Your guide to waterproof ratings, breathability & fabric technology.

June 26, 2015.nwt3k.10 Likes.1 Comment

How do waterproof/breathable fabrics work? What do waterproof rating numbers mean? Why does my waterproof jacket not always keep me dry? What is DWR? What is Gore-Tex?

We’ve put together this guide to help answer the most common waterproof and winter outerwear questions that usually require more in-depth, technical explanations.

A Brief History of Waterproof Fabrics

Waterproof / breathable fabrics were first introduced through outdoor apparel markets in 1978 when popular fabric manufacturer, Gore-Tex, introduced their popular laminate technology. Since then there have been many other waterproof / breathable laminates created such as eVent, Polartec and many generics. That said, most people still refer to the entire wp/br category as “Gore-Tex”, however, not all waterproof / breathable fabrics & rain wear is Gore-Tex – just like not all cars are Hondas and not all coffee is Starbucks. Gore-Tex is simply a historical brand with deep roots and a large presence within its product category.

How Waterproof / Breathable Fabrics Work

WP / BR fabrics are engineered to handle two tasks:

  • Repel and withstand moisture (keep you dry)
  • Provide an escape for perspiration vapors (remain breathable so your sweat moisture can escape)

How does this work?

waterproof breathable fabrics

Waterproof fabrics are most commonly composed of two or three layers including:

1. An outer layer called the “face fabric” – most commonly nylon or polyester. This outer layer is designed to repel, protect and look good. This layer is not waterproof, however it’s usually treated with a durable water repellant (DWR) to “bead” water.

2. A coated or laminated membrane – usually made with Teflon (ePTFE) or Polyurethane (PU). The job of the membrane is to keep water out but still allow water vapor to escape. This is accomplished though microscopic holes that are small enough to keep liquid water from passing through, yet large enough to let liquid vapor (your sweat) escape.

3. A tri-coat mesh – bonded to the inner service to create a 3-layer fabric. 2-layer fabrics can receive a separate fabric liner for protecting the exposed membrane and added comfort, but usually feature an exposed membrane.

Durable Water Repellent (DWR)

Almost all outwear fabrics are treated with some form of DWR. It’s designed to help repel water – most commonly seen when water droplets “bead” up on your jacket. This ultimately helps avoid fabric saturation and any added weight.

Over time through dirt, abrasion and body oils factory DWR finishes will wear off and you’ll need to re-apply an aftermarket DWR to sustain waterproofing in your jacket. There are many spray on DWR finishes available, we recommend NixWax spray on DWR finish.

Waterproof Ratings Explained: 5,000mm? 12,000mm? 20,000mm?

Waterproof Rating (mm) Protection Provided What it’s Good For
0 – 5,000 mm No protection to some protection 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
20,000mm + Rainproof and waterproof under very high pressure Heavy rain, wet snow, high pressure

Manufacturers (brands) use two numbers for describing the waterproof and breathability of fabrics: millimeters (mm) and grams (g).

Millimeters – is a measure of how waterproof a fabric is. In the case of a 10k or 10,000 mm fabric, if you put a square tube with inner dimensions of 1” x 1” over a piece of said fabric, you could fill it with water to a height of 20,000 mm (65.6 feet) before water would begin to leak through. The higher the number, the more waterproof the fabric.

Grams – The second number is a measure of how breathable a fabric is, normally listed in terms of how many grams (g) of water vapor can pass through a square meter (m2) of the fabric from the inside to the outside during a 24 hour period. In the case of a 15k (15,000 g) fabric, this would be 15,000 grams. The larger the number, the more breathable the fabric.

How are waterproof ratings determined?

Waterproof ratings are determined by the manufacturer (brand) or fabric producer in which waterproof testing is usually handled in-house or through independent labs. The most common testing procedure is the “static column test” described above. What most consumers are not aware of, however, is that there are a number of waterproof testing procedures in use today. In simple terms – two pieces of fabric from the same exact roll could produce different results depending on the waterproofing test conducted.

Today waterproof ratings are becoming more standardized, however do keep in mind different companies and labs may have different testing procedures that produce different results.

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How are breathability ratings determined?

Five main breathability test methods exist. Results from 4 tests are then extrapolated and converted into g/m⊃2;/day:

  • g = grams of water vapor that pass through.
  • m⊃2; = a square meter of fabric .
  • day (or 24h) = during a 24-hour period.

As a general rule of thumb, the higher the grams of water vapor that pass through, the greater the breathability.

Why is my gear not always “waterproof”?

All breathable outerwear designed for active winter sports and rain protection has various degrees of water resistance, but will eventually leak given enough water, time and pressure. Manufacturers define “waterproof” according to different standards, and like we’ve discussed, testing is not standardized. A rubber pair of bibs is completely waterproof, and may be the ideal garment for standing in a downpour waiting for the city bus, but if you tried to ski or snowboard in them, you’d be wet in no time from your own perspiration (sweat). Most normal jackets as well as big, tall and plus size winter jackets today feature waterproof, breathable fabric.

What is seam taping and why is it important?

Seam taping, sometimes referred to as seam sealing, is a heat applied thin waterproof tape that covers tiny holes made by the needle in the sewing process so the seams do not leak.

Outdoor waterproof outerwear can be either “fully taped” or “critically taped” – the difference is that a fully taped garment has every seam taped, while a critically taped garment has tape only on high exposure areas like the neck, shoulders, and chest. Without proper seam sealing you’ll get wet even with the best waterproof/breathable fabric.

What is GORE-TEX®?

Gore-Tex Membrane

Electron microscope photography of GORE-TEX® membrane

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®. 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.

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