Rain Gear Functionality

November 19th, 2023

There are a lot of misconceptions about the functionality of rain gear. In this post, I intend to clarify them. I hoped it would be concise enough for social media, but it felt like a little more detail was needed, so I'm expanding here and will summarize elsewhere. I mostly use the term "rain jacket", but know that the same information applies to most rain pants as well.

Rainwear construction

Since the 1970's when GORE-TEX became available, many other brands have copied the technology, and almost all rain gear of decent quality has been made on a similar foundation: a waterproof/breathable (WPB) membrane laminated to a face fabric. The membrane is a thin film with pores small enough to keep liquid water from entering, but large enough to allow water vapor to slowly escape. Most membranes strike an appropriate balance and resist not only rain, but also wet bushwacking with ease.

WPB Membranes alone are not very robust, so they are laminated to a face fabric made of woven nylon or polyester. The face fabric protects the membrane and makes the jacket look more presentable. This is the basic 2-layer construction. The result is a fabric that resists abrasion and is fully waterproof and windproof, but allows moisture from sweat to escape slowly. It is easy to overwhelm the rate of escape by sweating too hard, but the breathability does work. Any jacket that employs this type of fabric and has properly taped seams is waterproof enough to protect the user from rain, and remain so for multiple years.

With use, the membrane can wear out from interior abrasion against the user's body. To solve this problem, most higher-end WPB jackets are constructed with a layer of liner fabric laminated to the inside. This 3-layer construction means that the membrane will be protected from both sides and should remain intact for the entire life of the jacket. Adding a third layer to the inside of the jacket does add some weight, packed bulk, and cost, so many mid-range jackets go for a compromise instead. Known as “2.5L” fabrics, these feature a sprayed or printed-on protective liner that has a plasticky feel.

Rainwear treatment

Unfortunately, there are some drawbacks to the usual WPB design. Since the exterior surface of the face fabric is slightly textured and nylon is absorbent, it is possible to saturate it. Users will clearly be able to see this phenomenon, because it darkens the color. When this happens, breathability is reduced to zero, because although sweat vapor can pass through the membrane, it cannot squeeze its way through the wall of saturated nylon. The presence of water on the surface also makes the fabric cold. Even at rest, humans are always sweating, and more so if exercising hard. The implication of this is that warm sweat vapor is on its way towards the exterior of the jacket when suddenly it hits a cold wall and condenses into liquid. The inside of the jacket is now wet. This is the infamous phenomenon known as "wetting out".  Wetting out is not a failure of waterproofing, it is a failure of breathability.

The go-to solution to this problem has been to apply a hydrophobic treatment to the face fabric, known universally as Durable Water Repellency (DWR). DWR coatings have been around since the 1940s. These chemicals are applied to the surface of nylon fabrics to prevent water from absorbing into them, forcing the water to "bead up" instead. Water beading up on the surface of a garment is a beautiful thing, and has a very important purpose. Without the ability to shed water, breathable jacket membranes are only breathable while it's not raining. In this way, the success of WPB membranes for rain is built on the existence of excellent DWR treatments. Membranes do work well without DWR when it’s not raining, but in most non-rainy situations,  their breathability rates are too low to be tolerable during activity anyway (see the final section for more detail). 

DWR treatments aren’t just hydrophobic, they're also oleophobic (oil resistant), a property that gives the garment a degree of stain resistance. Because stain resistance is a pretty desirable trait, and because water beading is a beautiful (and marketable) sight, manufacturers started applying DWR to other types of clothing too, such as windbreakers and hiking pants, even if it isn't essential to their function. This allows them to market other garments as "water resistant" when they otherwise wouldn't be. Immense confusion has been created among uneducated consumers by this term, which prompts the thought, "This jacket should be good for rain". Well, a water-resistant jacket is specifically not a rain jacket. Confused now?

Treatment failure

The first problem is that DWR treatments are made of polyfluoroalkyl substances (PFAS), which have been receiving a lot of attention lately. They have been justly classified as "forever chemicals", which means they not only last forever in the environment but also accumulate permanently in the body. Many studies have found that PFAS is correlated with a variety of human health problems. Exact causality is unclear, but they certainly aren't good for us. You may or may not be worried about the health implications of PFAS, but that doesn't matter much anymore. PFAS have been slowly getting eliminated from certain categories of products (e.g., pizza boxes) for years. But big changes to the PFAS industry are about to happen. As soon as 2024, multiple states will not permit the sale of any product containing any amount of PFAS above a tiny trace threshold. According to Alex Lauver, the Senior Director of Materials, Innovation, and Sustainability at Outdoor Research in this podcast, this will influence the apparel industry in two ways: 1) States like California and Washington are on the list, with economies so large that when they outlaw something, manufacturers may as well not make it anymore, and 2) Because production and marketing regimes work years in advance, PFAS will start to disappear even before 2025.

The logical solution to this problem is to develop a non-PFAS alternative to DWR. Surely science could do that? Well, they're hard at work on it, with some results. Most new DWRs are yet to be released, so we'll have to wait and see what they come up with. But it's a hard nut to crack. There have been reports of product designers telling their sales reps that consumers will be shocked when the new high-quality rain jacket they bought from a reputable brand just doesn't bead water as well. Unfortunately, the qualities that we seek from DWR are integral to the definition of PFAS. Literally, the FDA definition says: "polyfluoroalkyl substances (PFAS) are chemicals that resist grease, oil, water, and heat", which to me implies these properties may be difficult to find elsewhere.

Dodging the question

The future of rain gear is unknown, but the present is dismal anyway. The reality is that being out in the rain is pretty miserable unless you employ Luc Mehl's 3 tricks to get through bad weather: "yellow lenses, caffeine, and dance music".  I've never tried the first, but I do find the company of good friends to boost morale as well. Even the most breathable membranes with perfect DWR aren't enough to prevent you from getting wet from the inside. Hikers are often torn between being too hot with a jacket on, or too wet without it. So, what do we do? One solution (and my personal favorite) is to bypass the problem entirely by shifting the emphasis to being warm rather than dry. Let me explain.

First of all, we need to acknowledge that being wet is not necessarily the end of the world, depending on air temperature. In warm weather it can often be more comfortable to allow yourself to get wet and dry later when the rain stops or you get to camp. Achieve this by simply wearing a quick-drying shirt, or, in select circumstances, going shirtless. Speaking of getting to camp, once you stop exerting yourself, wet clothes can indeed make you cold. To avoid hypothermia, set up a shelter and/or put dry clothes on. But even in summer the rain can be cold, and we’ll sometimes find ourselves not exerting much because we’re eating a snack or treating a blister. What do we do in these circumstances? Well, wear a rain jacket. But stop worrying about being perfectly dry on the inside.

Of course, activity in most cold and rainy conditions requires a rain jacket to stay warm enough, but being sealed up inside a non-breathable shell is too warm and sweaty. If breathability is an unrealistic goal but we still need to keep rain off, then how do we mitigate sweat? Focus on the sealed up part and ventilate. The only sustainable way to regulate core temperature and allow sweat to evaporate is to increase airflow. Many rain jackets are designed with adjustable hems, hoods, and cuffs, loose fits, full front zips, and pit zips. The more these things are taken to the extreme, the better. My green Arc’teryx jacket pictured above has only two of these things, and it doesn't keep me very comfortable. On the other hand, ponchos work great if you're not bushwacking, it's not windy, and it never becomes cold enough that you actually do need to be sealed up. Because I often encounter these situations they’ve never been an option for me, but serve many users well.

Mitigating the flaws

If we reframe our perspective on the pros of laminated WPB jackets, then we can start to address their cons. The main problem is that saturated face fabrics are heavier and take longer to dry, making the user cold. They can also delaminate. Assuming that they aren't actually breathable at all when the face is saturated, then maybe there are better fabrics out there? Enter my latest clothing interest, impermeable rainwear.

Many fabrics exist that solve this problem. The lightest options used in rainwear are siliconized nylon (silnylon) or polyester (silpoly) and Dyneema Composite Fabric (DCF), all of which are used in tents. None of these have any breathability, but they can be made into rain gear that ventilates. The water beading effect is permanent with DCF because its waterproof film is on the outside, so drying is nearly instant. But like WPB laminates, DCF is also a type of laminate that requires packing care and the exterior membrane is fragile. In siliconized fabrics, the weave of the fabric is fully impregnated with an inert and long-lasting silicon treatment. They usually bead water excellently, silnylon doesn’t absorb much, and silpoly absorbs even less. Siliconized fabrics are known for their ability to be stuffed carelessly into tiny sacks, left there for months, and be totally fine (as we do with tents). Be aware that many cheaper siliconized products are coated on one side with PU rather than silicon, allowing them to be seam taped. A deep dive on fabric coatings is published by tentmaker Slingfin here. PU coatings do break down in storage, especially if wet. So, the longest-lasting jackets will be made of pure siliconized fabric, but some users may want the seams sealed manually.

Currently, only a few fringe options exist for purpose-built impermeable rainwear of reasonably light weight, but the industry is rapidly gaining traction as people realize the flaws of DWR and the shortcomings of laminated jackets. The biggest proponent of the philosophy is probably Timmermade, while the most popular is Lightheart Gear. Well known hammock company Warbonnet also makes an option, and I chose to try one from AntiGravityGear (AGG). These are all small brands, but as PFAS DWR goes extinct I hope to see more widely available and refined designs. Another advantage of these products is that they are often far less expensive than a laminate jacket of equal quality. My AntiGravityGear jacket is currently $99.

So, how well does it work? Well, longevity is still unknown, but I've used similar fabric in tents enough to be confident it will remain waterproof for a long time. It's a little thinner than my Green Arc’teryx shell, so I'll have to be careful, but all clothing of reasonably light weight requires some care. As long as I don't rip it open on a branch, it should last until the zippers fail, which will be a long time.

I tested it extensively in both light and heavy rain this past summer throughout the Wyoming Rockies and found it to indeed be plenty waterproof, absorb less water than my green Arc'teryx jacket, and be significantly better for high exertion activity due to the ventilation features.

There is one obvious downside: it's pretty hideous. I think I probably got the worst of the bunch here. The only color options were black and orange and I didn't want to look like a trash bag. The high visibility is indeed helpful for foggy backcountry conditions, so I'll continue tolerating it. The cut is far from flattering, but it's comfortable. The hood on this model is also somewhat ridiculous. It's big enough to be "helmet compatible" which seems excessive for an ultralight jacket like this, and means it has a bunch of extra material. The back-of-head volume adjustment doesn't work well, but the shock cord face cinches do. The visor is so flimsy it's useless, but over a hat it works just fine. AntiGravityGear's website says they have updated the hood design, so perhaps it's great now. In summary, I'll keep this jacket for backcountry use and keep my high-fashion Arc'teryx for around town. They really do have different functions.

Additional downfalls of an impermeable garment are less clear. For one, there are often situations when people are wearing rain jackets that aren't fully saturated, such as in light rain that only saturates the hood and shoulders, or in dry windy conditions. In these cases, the dry jacket still allows vapor transfer through the membrane. But I personally don't find the breathability of dry WPB jackets to be adequate for moderate activity unless temperatures are cold. Going to an impermeable jacket doesn’t feel like a huge difference. 

I have worn the AGG jacket while exerting moderate hiking effort through Kanab Creek as the cold morning breeze blew and I was comfortable. To be clear, this cold situation was rare on this trip. I was actually not warm enough in just my sunshirt.  A better option for cold wind is to wear a windshirt. The 8oz weight of the AGG jacket allows me to bring my $15 Dooy windshirt for a total of 10oz, an incredibly versatile combo for 2oz less than my 12oz Arc'teryx jacket. The Dooy windshirt is not totally windproof, but it is more wind resistant than a hiking or sun shirt. Windshirts like this are an incredibly comfortable layer for strenuous hiking in cold wind and definitely have their place beside a rain jacket. I chose not to bring the windshirt on the Kanab trip to simplify my kit and because the daytime temperatures were almost always above 60F. When it was below 50F, the impermeable jacket did just fine.

Unfortunately, I also wore the AGG jacket around camp on many July evenings in Yellowstone for protection from mosquitoes. It was fine for this use, because breathability demands at rest are low. One evening though, when it was cold enough to wear my down puffy but the bugs were still out, I layered the two. After a couple hours I went to bed and noticed the shell fabric of the puffy was damp from condensation inside the shell. If my down puffy had a hood, I wouldn't have needed to wear the raincoat at all, making this scenario pretty niche. You can wear down insulation under an impermeable jacket, but even wearing down under a WPB shell requires consideration of: 1) if it will get wet from sweat, 2) if it will dry, and 3) the consequences if it does not dry. In my case the down jacket dried quickly inside my sleeping bag. There are plenty of synthetic insulations that dry rapidly if damp, and therefore work great under an impermeable shell. For moderate activity in cold rain, I particularly love a Polartec Alpha fleece.

Conclusion

The reason users get wet inside rain jackets is probably not a waterproofing failure, but a breathability failure. All good jackets are waterproof without treatment, but rely on DWR coatings to maintain breathability. DWR coatings are about to get crippled because they are made of PFAS; which will soon be banned fully in many economies. DWR alternatives are not currently promising, but that’s okay because DWR was a mediocre solution anyway. Ventilation features are better than betting on breathability, and deserve to be prioritized. If we give up on breathability, we can have a better experience using alternatives like the affordable, light, and long-lasting fabrics used in tents. When it's cold but not raining, it’s often more comfortable to use a super breathable wind shell instead. The combination of an impermeable layer and a windshirt probably costs and weighs less than a traditional rain jacket, and provides a greater range of performance.