The Truth about Gortex

By: bowhunting biologist Wade Nolan
Sponsored by: Whitetail University, Bear Archery, Dries Visser Safaris, ATSKO, Mountaineer Sports & Shwacker Broadheads

Water resistant outerwear, waterproof shells, breathable fabrics, they all say they deliver what we want. All we want is to simply want to stay dry when out in the boonies. But do they deliver? Is the techie part really techie enough to keep me dry when I’m in a treestand in an all day cold drizzle? The facts may surprise you. The short story is that they can keep you dry and comfortable if you understand how they work and what you need to do to keep them working.

Waterproof and breathable can be the difference between life and death in some environments. Tim, at a mountain pass in Alaska is dealing with 35-degree driving rain. Wet here can lead to dead.

Gone are the days of the yellow rubber slicker that didn’t leak but you got soaked from perspiration. Granted some applications still call for this waterproof approach. Watch the crabbers out in the Bering Strait in Deadliest Catch try to stay dry and you’ll not see breathable fabrics. They need a barrier that is non-permeable like rubber. But most of our outdoor endeavors call for some level of comfort and fabrics like Gortex have met the call.

Situations where these fabrics are important are broader than just during a rain event in a treestand. Many of the new microfiber fabrics and laminates allow for a generous air flow, have wind-breaking properties and still shed moisture. Cold winter conditions may require a breathable fabric as well.

Just last weekend I joined some friends on an ice fishing expedition on the Bay of Quinte on the north shore of Lake Ontario. We had all sorts of weather across five days. The temp ranged from 43-degrees to 9 above. We had sunshine, rain and snow. The wind ranged from dead still to 28 mph. the only thing it didn’t do was get suntan hot. This is where breathable fabrics really shine.

A variety of weather conditions call for breathable raingear that will both allow body moisture to escape and serve as a personal wind break. These fishermen are also bowhunters who rely on some of the same gear for late season whitetailing.

The waterproofing level of fabrics is rated by some ASTM tests that fabrics are subject to. To be categorized as truly waterproof, a fabric must provide a high level of sustained water protection during the harshest conditions. In a laboratory setting, the more effectively a fabric resists the entry of moisture under pressure, the higher its waterproof rating will be. Waterproof ratings are measured in two ways, both related to maximum water-pressure resistance: Pounds per square inch – a pressure test and a rainfall equivalent measured by mm/24 hours.

The “mm/24 hours” rating refers to the amount of rainfall a fabric can withstand in a single day. Thus a 10,000 mm waterproof rating means the garment can withstand over 32 feet (10,000 mm) of rainfall in a single day without letting moisture in. Don’t forget that the sealing of seams and stitching plays a practical role here. For either rating, the higher the number, the more waterproof the item will be. For example, a fabric labeled to resist 5 psi of water pressure without leaking is not as waterproof as a fabric that resists 10 psi of water pressure; a fabric with a waterproof rating of 10,000 mm is more waterproof than a 5,000 mm fabric.

Sportsmen often deal with shifting weather patterns. All of these pics were taken the same day spanning the AM to PM. Morning rain and then plunging temps by evening. One strategy is to hide in your ice fishing hut like a clam but that's not always an option.

Commonly used water-resistant fabrics withstand between 3 to 5 psi of water pressure, which is fine for a short, light rainfall (which only generates 2 psi of water pressure). Completely waterproof fabrics like Gore-Tex® or eVENTwithstand up to 40 psi of water pressure, and test out at 28,000 mm/24hours. But what about the breathability of these fabrics? To better understand this process look at this diagram of how the fabric layers play a role in moving water vapor away from your body.

This diagram explains how these high tech fabrics like Gortex work. Note the water vapor only moves out if the outer layer is beading water.

Here is how the breathable fabrics work. Although there is some variation in their approach they basically are a sandwich of fabrics layers. The key to their performance is a layer of Teflon like membrane that contains millions of microscopic “pores” per square inch. These pores can be up to 20,000 times smaller than a water droplet, but are much larger than water vapor molecules. This pore size allows the membrane to be completely waterproof from the outside while still allowing moisture to escape from the inside, making the garment breathable. The force that actually moves the water vapor is a temperature differential between the inside (you) and the outside (the wild blue yonder).

The magic of breathable fabrics is made possible by a temp differential between the inside and outside plus a totally clean, residue free outer shell and open microscopic pores in the membrane. In the same way that if that hole freezes over you can't get your walleye up through the ice, the closed pores in the membrane will stop moisture from passing through.

The water vapor is able to move through the fabric only if the coast is completely clear. By that I mean that the outer most shell must not be coated (we call it sheeted) with water. Only if the outer most layer is beading water can the fabric breath between the water beads. The DWR (Durable Water Repellant) is applied to the outermost shell and this is where a lot of the failure begins. When new it causes water to bead up which is a good thing. Failure occurs when it is not beading but is coated uniformly with a layer of water. It’s the wet look that can generate total failure.

An outer shell sheets water because the DWR fails. Here is why it can fail and why I explained all of this to you. If the outer shell is dirty it fails to bead. If it is oily it fails. And the most common cause of failure is soap scum. That’s the stuff that makes the ring when you have a tubby bath. That is soap scum but there’s more. Soap can be either your friend or your nemesis. If the shell is not beading it may be dirty, and it doesn’t have to be very dirty to fail. If you wash the garment with almost any soap you will gum it up more and you’ll think the garment is worn out which it isn’t. Laboratory tests done at Clemson University School of textiles have demonstrated that most detergents leave a residue of scum on the fibers of virtually any cloth. If you use a detergent on your expensive breathable rain gear you will likely scum it up and cause it to fail even more.

Only Sport-Wash will keep your breathable outerwear breathing and you dry.

This detergent residue is not visible to the naked eye but it is clingy and bonds to fibers and surfaces. It has even been proven to add weight to any garment during a washing/drying cycle. This residue will also clog up the microscopic pores in the breathable fabric. Now you might as well put on a garbage bag with the arms and head cut out. It will breathe just as good. The solution is to only wash your breathable raingear with SPORT-WASH by ATSKO. This engineered detergent has been tested to clean these garments and then rinse completely out so your DWR coating will bead and the breathable membrane can breathe.

The other application of this principle can be experienced when you’re out in the winter weather like I was last weekend ice fishing in Ontario. Breathable waterproof outerwear worked to vent perspiration and keep us warm because we’d washed/cleaned them in the right stuff.

These bowhunters are self-medicating their outdoor passion in mid winter with walleyes through the ice. The breathable outerwear they are wearing made the ordeal bearable and even fun.

The truth about Gortex and all of the new breathable fabrics is really simple. They are high tech and they require a high tech engineered detergent to keep them ticking and you happy.

ATSKO  Sport-Wash is available at almost all outdoor sporting goods stores and the big W-Mart.