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Waterproof fabrics are nothing new. Wellington boots were quite the rage with our pasty friends across the Atlantic when we were rootin', tootin', and shootin' out West. But what anyone who has trudged around in a pair of gumboots and what any exhibitionist in a Mackintosh will tell you is that these materials are incredibly uncomfortable. PVC and rubber are stuffy, sweaty, and smelly. They don't have those magical words that are so important in the outdoor industry—waterproof breathable.

Waterproof

Most people will say: “With waterproof fabrics, the pores are big enough for water vapor to escape, but small enough to prevent a liquid from passing through.” That sounds pretty simple—akin to sifting through soil or draining your pasta.

As it turns out, pore size alone doesn't make a fabric waterproof. Rather than having the perfect pore size, garments such as Patagonia's Rain Shadow Jacket utilize a membrane with a high surface energy level—hydrophobic—that repels water with such force that it takes a great deal of pressure to break through. While the pores contribute to the hydrophobic quality, it is not necessarily the size of pore that matters, but the strength of the repelling force—in our case, hydrophobic force—in relation to the incoming force, or water pressure.

Waterproof Ratings

Even though most fabric manufactures calculate waterproof figures in their own labs, they generally use similar testing methods, so you can take their waterproof ratings at face value: the higher the number, the better the garment resists water.

According to government standards, the water-force a material must withstand in order to be deemed 100% waterproof is 25 PSI. You can zip up a Marmot Essence Jacket, whose PreCip Plus material has a rating of 45 PSI, sit in the rain (7 PSI) and stay dry as a bone. Step in front of a fire hose for an hour and if you can stay on your feet, you'll get wet. Simple.

Yet outdoor companies don't always use PSI to highlight waterproof quality. Instead they tout large figures that have a more tangible meaning than pounds per square inch. For example, the Cloudveil Zorro Jacket has a waterproof rating of 10000mm (10K). This figure represents the amount of rainfall the fabric can take in a 24-hour period before the wearer gets wet. In Imperial terms, the Zorro Jacket can withstand nearly 33 feet of rain in 24 hours. Seattle, by comparison, gets 36 inches of rain a year.

In a closed system, a 20k rated jacket will retain its waterproofness longer than a 10k jacket. However, out in the field any jacket's waterproofness can degrade over time until the garment eventually becomes a clammy, wet mess. Oils, dirt, sweat, and other contaminates find their way into the fabric, weakening the hydrophobic forces until the water repellency becomes so poor that water can just break through to the other side. To combat this, Gore-Tex and the like coat their hydrophobic material with additional impermeable membranes. While this prevents contamination and ensures waterproofing, it has detrimental effects on that other magic word—breathability.

Breathability

Breathability has always been the thorn in waterproof's side. Hydrophobic membranes perform wonderfully in a closed, contaminant-free environment but falter when you throw your sweaty body, dirt, and grime into the equation. The solid polyurethane and DWR coatings that cover the waterproof membranes strangle breathability and create an obvious trade off: ensure breathability at the expense of waterproofness, or guarantee waterproofness while sacrificing breathability.

The problem with rating breathability is that, unlike waterproof's rain and pressure tests, there is no standard testing method to measure the movement of water vapor. For example, the Oracle Jacket's Precip Plus material's breathability rating is 12,000g while The North Face Prophecy Jacket's HyVent's is 877g. Does that mean that the Oracle breathes 15 times better than the Prophesy? Absolutely not. We have no way of knowing if Marmot and The North Face performed the same test—in this case, they probably didn't. Gear manufacturers generally use the standard that makes their product look the best. When choosing a waterproof product, use the manufacturer's rating as a general tool to compare breathability rates within a specific brand.

Bottom Line: take a manufacturer's breathability rating with a massive grain of salt.

Image by Steve Rafuse

It is important to realize that waterproof and breathability ratings are only part of the greater issue. View them as a general guide to narrow down the playing field and then use the four interrelated factors of breathability/ventilation, weight, durability, and price to decide on a product. Take the OR Celestial and the Marmot PreCip Jackets, for example. The Celestial and PreCip have similar weights and waterproof ratings. However, the OR Celestial is much more breathable and durable than the PreCip, but costs about 2 1/2 times as much.

Since you'll never find a waterproof product that is highly breathable, ultra lightweight, incredibly durable, and cheap, you need to determine which of these factors are most applicable to the activities you'll use the garment for, choose accordingly, and run out into the rain.