Waterproof Jackets: Get Your Learn On
Taking a look at waterproof breathable jackets can conjure up thoughts of a day you were happy you had your waterproof jacket or not. The first thing to note is materials such as rubber or metal are waterproof. Fabrics are not waterproof; they are highly water resistant. Say that again one more time just so you remember it the next time you wonder why your jacket or boots are leaking. If water can eventually carve out a canyon through rock, it will eventually get through your jacket. Now some fabrics will be more resistant (“proof”) than others and even between these jackets some will stay that way longer than others. More recent in the history of textile is the creation of waterproof breathable fabrics. These fabrics are a delicate balance between being highly water resistant and letting moisture back out. Below I will try to explain all of this.
In this article, I will discuss many of the different types of Waterproof membranes. I am not going to try and determine what ones are the best/worst of the technologies. I will try though to outline the technologies as each membrane may have very different performance across different garments.
How Waterproof/Breathable Jackets Work
Waterproof/Breathable jackets have been around since 1978, almost as long as me. This is when Gore-Tex was introduced. Since this time there have been other laminates that have been created but most still call waterproof jackets “Gore-Tex”. Waterproof/Breathable jackets are made to do two things: block water from getting in and allow perspiration to get out.
The inside of the jacket can use one of two technologies to become waterproof and breathable. The first technology is laminates. Laminates are created when a waterproof/breathable membrane is bonded to the underside of an outer fabric. The other technology is coatings. Coatings are liquid solutions that provide waterproof/breathable characteristics when spread across the inside of the outer fabric. Coatings and laminates will be discussed in more detail later in this article.
The outside of the jacket also has a lot to do with the waterproof/breathable characteristics. All rainwear exteriors are treated with a DWR (Durable Water Repellant) finish. This finish only affects the exterior of a garment, and not the laminate or coating. A DWR treatment causes water to bead up on the outside of the jacket and does not allow the face fabric to become saturated. DWR finishes can deteriorate over time due to wear, dirt, or laundering. DWR will be further discussed later in this article.
Why Waterproof Jackets feel clamy
Laminates at the core are a membrane. Membranes are made from stretched polytetrafluoroethylene (ePTFE or PTFE), polyurethane films (PU), polyester films, and polyethylene (PE).
PTFE is a fluorocarbon solid, as it is a high-molecular-weight compound consisting wholly of carbon and fluorine. A PTFE Membrane has a super thin web-like structure. W.L. Gore estimates the PTFE has about 1.4 billion pores per square centimeter. Even with all these pores PTFE still remains waterproof/breathable as the pores are too small for water to pass through but large enough for water vapor to pass out of. PTFE is hydrophobic, water cannot wet PTFE. It does not wet as fluorocarbons demonstrate mitigated London dispersion forces due to the high electronegativity of fluorine. PTFE has one of the lowest coefficients of friction against any solid. What this means is PTFE has low "surface tension." Its application to waterproof/breathable fabrics is that this low surface tension compared to the high surface tension of water makes water pull together into large drops on the surface of PTFE. When water consolidates into large drops on the surface, the drops want to roll off the surface as there is not much energy holding them on. Therefore, water can only penetrate the fabric two ways; either by tremendous force or the surface of the PTFE is altered by being contaminated by dirt and oils.
Contamination is the main reason why a PTFE membrane will leak. Contaminates such as dirt, oils, sunscreen, insect repellant, or other foreign matters can easily alter the surface of unprotected PTFE. Companies have had to come up with different methods for protecting the laminate from these contaminates. Generally, there are two ways in which PTFE laminates are protected: either by adding a protective finish or attaching a super-thin PU membrane. Different manufacturers are employing these different processes and below we will go over each of those.
Polyurethane on its own is also very thin, but it cannot be as thin as when attached to a PTFE outer membrane. PU is a polymer composed of a chain of organic units joined by carbamate (urethane) links. Polyurethane is often used as a backer for PTFE laminates but can also be used on its own as a laminate. Polyurethane moves moisture through an adsorption-diffusion-desorption process. This means it attracts water molecules to the inside of the fabric (adsorption); the molecules eventually seep through the fabric (diffusion); and the molecules then evaporate off the outside of the laminate(desorption).
Polyurethanes have been more recently being made thinner than before and may be narrowing the gap to PTFE laminates in terms of performance. PU can be formulated in a wide range of products, which means it allows the mad scientists at each manufacturer a great deal of opportunities to come out with the latest and greatest.
While not as widely used, polyester-based membranes are gradually growing in usage. Polyester films are most often attached to polyether films. The polyester film on the outside is hydrophobic, and the polyester film is hydrophilic. This creates a process of adsorption-diffusion-desorption just like PU laminates. Polyester laminates however can be made extremely thin, so they claim to be faster at transporting moisture because of that. The industry view of Polyester films is that it is lagging slightly behind PU laminates in breathability. They do offer a greener alternative. They can be recycled as long as they are attached to a polyester fabric which can also be recycled.
Polyethylene is rather new to membranes in outdoor applications. Polyethylene is a thermoplastic polymer consisting of long chains produced by combining the ingredient monomer ethylene. UHMWPE is polyethylene with a molecular weight numbering in the millions, usually between 3.1 and 5.67 million. The high molecular weight makes it a very tough material. Because of its outstanding toughness and its cut, wear and excellent chemical resistance, UHMWPE is used in a diverse range of applications. Due to its high strength, the membrane can be made really thin and therefore be lighter.
Coated rainwear uses liquid based polyurethane applied to the fabric. Coatings can be applied in a manner to create a completely waterproof and non-breathable jacket as well, but we are going to focus on the breathable versions here. They can be done two ways. The first method is by a microporous coating. This coating has many microscopic channels that can transport water vapor through the fabric. To create these channels the coating can either have a foaming agent added to create air bubbles in the coating or the coating can have solid particles added to it. The solid particles create spaces where vapor can transport out by creating fissures through the substance when the coating dries. The second method is by monolithic coating. A solid, hydrophilic layer that transports moisture via the adsorption-diffusion-desorption method as described above. Both these methods are indistinguishable unless noted by the manufacturer. Their performance is also very similar. Coatings as a process are much less expensive than laminates. Coated jackets therefore can retail for much less. They are great options for less technical applications and every-day usage. They have been average to above-average performance and make a good option for a lightweight waterproof-breathable jacket for less technical adventures.
Laminates and coatings are not only delicate but also subject to contamination. In order to protect them, jackets are made with multiple layers with the laminate or coating inside. For this article, I am going to cover 2-Layer, 2.5-Layer, and 3-Layer construction. 1-Layer jackets also exist but they are either not fully waterproof or breathable.
2-Layer Jackets are generally the most affordable waterproof/breathable jackets. They are constructed by applying a membrane or coating to the inside of the face fabric. To protect the coating or membrane and inner liner fabric is stitched into the inside of the jacket. This liner fabric is often loose hanging and separate from the outer fabric, usually made from mesh. 2-Layer jackets are generally more bulky, heavier, and less breathable then other designs. These jackets also generally have more pockets and are better options for less demanding conditions.
2 Layer Example
2.5-Layer jackets are often the lightest weight offerings available. They use a lightweight face fabric, a membrane or coating applied to the backside of the face fabric, and a bare-minimum protective inner layer. This inner layer is more like a sheen than an actual layer which is why it is called a half-layer. Often, this inner layer may be a series of dots, grid pattern, or scattering of resins to protect the interior from abrasion. 2.5-layer jackets are lightweight but are also a bit less durable. They are best as options when weight is paramount or as an emergency shell in the pack. Furthermore, if abrasion resistance is not a concern, then a 2.5-layer jacket would be a good option.
2.5 Layer Example
3-Layer jackets are the most durable jackets out of the group. You will find no coatings in this category, all the jackets in here will be made with laminates. 3-Layer jackets are made with a laminate sandwiched between and outer face fabric and inner body-facing fabric. 3-Layer Jackets can be made, like other jackets, with varying thickness of outer face fabrics. It is also common to find the jackets in this category to be built with technical cuts and features. 3-Layer jackets are good options for the most demanding adventures such as serious climbers and backpackers. They can take a beating and keep on performing. Jackets in this category aspire to high breathability, high durability, and relatively low weights. This is also the most expensive of the categories covered here.
3 Layer Example
While companies have issues on agreeing how to measure how breathable a fabric is, they all agree on how to measure how waterproof a fabric is. The test is called a water column test. A 1-inch diameter column of water is stacked on top of the fabric, and the amount of water in millimeters is increased and measured until the fabric leaks. The higher the number the more water pressure it takes until water is forced through the membrane. The number is usually published as “20k mm” or “20,000 mm waterproof." While manufacturers agree how to measure waterproofness they cannot agree on what constitutes waterproof. The other issue is most manufacturers do this test before the membrane goes to fabric.
To give a bit of reference to the measurements of waterproofness:
- 704 mm = 1 psi
- Wind Driven Rain is about 2 psi or 1,408 mm
- Hurricane Force Rain is about 10 psi or 7,040 mm
- Fire Hose from 30 ft is about 16 psi or 11,264 mm
- 180 lb person sitting is about 8 psi or 5,632 mm
Seam tapings is just what it sounds like. The stitching and joining of fabrics creates weak spots in the waterproofing at the seams. Seam tape uses a polyurethane adhesive to block these vulnerable locations. In general, the seam tape does not carry the same rating of the rest of the jacket and are also subjective to the quality of application. If the tape has been applied poorly it may leak. There are also a couple of different types of taping that one needs to be aware of: full seam taping, critical seam taping, and welded seams. Full seam taping is pretty straight forward. It means all the seams of a garment have been taped. As far as seam taping goes this is the most waterproof option. Critical seam taping means only the seams deemed important on the garment have been taped. This normally constitutes the shoulders, chest, and sleeves in jackets. While this does leave some areas vulnerable, most of the jackets that feature this type of taping are skiing and snowboarding jackets. The last type of seam taping is not technically seam taping. Welded seams are a different type of construction method in which the fabrics are joined together by gluing or sonic bonding. This means there are no holes or gaps in the fabrics created by stitching and therefore, the jacket is water tight. As with seam taping the quality of the workmanship matters greatly but since there is no use of tape a well-made jacket can be even more waterproof than a taped version.
Breathability ratings are tough to agree on. There are several tests that measure breathability. That is, the rate at which moisture vapor moves through a fabric. No one agrees on which method is the standard, and brands tend to use the test that portrays their products in the most optimum light. To help you better understand the different test and what they mean I will try to explain them below.
One thing to remember that the inside of a jacket is a micro climate. The temperature and humidity levels will vary widely on the amount of exertion, any venting on the jacket, the exterior conditions (i.e.: temperature and humidity), and layers worn by the user. While these tests may give you an idea of the breathability, it is possible for fabrics to have equal results in one test and different results in another. Take these tests as a general idea but it is truly difficult to garner any hard information from them.
DMPC (Dynamic Moisture Permeation Cell) test
This test takes into account different humidity levels. It measures the amount of moisture that moves through the fabric at these different levels. The results of this test are presented in graph form, and manufacturers want to see horizontal lines that indicate consistent levels of breathability across all humidity levels. How this test is done is by stretching fabric through a chamber, creating two separate cells. Humidity and pressure are controlled and measured on both sides. Proponents of this test say it best mimics changing real-world conditions. Of the three tests mentioned here, this is the least likely seen when brands market their jackets. DMPC was developed by Dr. Phillip Gibson, a civilian scientist working with the US Army. It is currently what is used by the Military to test jackets for their use.
MVT (Moisture Vapor Transfer) test
The test measures how much moisture (sweat) moves through a fabric over a given amount of time. The results are normally stated as grams per square meter per day. The larger the number the greater the performance. This test is conducted by stretching the material over a cup. This process can be done several different ways: inverted cup, upright cup, membrane touching or not touching the water. Then the volume of evaporated water is then measured. This test is commonly used, but as you can see has many problems when you go to compare membranes.
RET (Resistance to Evaporative Transfer) test
This test is also known as the “sweating hot plate test." The test measures how much a fabric resists letting moisture vapor through. Since performance is based on how much vapor is blocked, the lower the number the better. The test is performed by first saturating the fabric. The fabric is then placed over a heated and porous metal plate. This plate is intended to mimic human skin. The volume of the evaporated water is then measured.
Wind Resistance/Air Permeability
Air permeability has become a buzz word in waterproof/breathable jackets over the last years. It is generally displayed in miles per hour (mph) or cubic feet per minute (cpm). Wind resistance and air permeability are one in the same as they are a measure of how much air can pass through a fabric over a certain amount of time. Until recently this was not associated with waterproof/breathable jackets as none of them were air permeable. However, since it has been more popular recently I will include it in this article.
The most common test for this is the Frazier Air Permeability Test. This test measures the amount of air (in cubic feet) that can pass through 1 square foot of a fabric sample in 1 minute at a pressure differential equal to a wind speed of 30 mph. Most waterproof/breathable jackets have ratings of zero on this test but more recently some have a bit of air permeability. This can have a great impact on the breathability of a jacket. Each of these technologies will be discussed more below.
Virtually, all rainwear is treated with a DWR (Durable Water Repellant) finish. A DWR finish is the first protection from the outside elements. The DWR finish is applied to the outer face fabric fibers to prevent water from saturating the exterior face fabric. Without this finish, the outer face fabric can get waterlogged; making it heavy, sagging, and less breathable. They are subject to contamination and can wear out but unlike the inner materials of a jacket, a DWR finish can be renewed.
DWR finishes do not inhibit the breathability of a jacket. They do not coat a fabric but rather bond to the fibers of it. This still leaves the little holes between the fibers which are important to breathability. DWRs consist of a chemical compound normally containing fluorocarbons but silicone and hydrocarbons are also sometimes used.
How DWR Works
DWRs work by increasing the contact angle or lowering the surface tension of the fabric. Just like in laminate technologies, water will form a larger droplet due to the lower surface tension of the fabric. This droplet will then just roll right off the surface of the jacket and not soak in as it would if it was allowed to sit on the surface. DWRs do come in different effectiveness ratings. This is done by a spray test where the amount of fabric with no water attached to it is measured after a number of washes. The rating will be displayed like this: “90/10”. This rating would indicate the 90% of the garment was water free after 10 washings. Not all manufacturers publish the performance ratings of their DWR finishes but a basic guide would be good is 80/10, excellent is 80/20, and superior would be 80/50-100. To test your DWR you can do a spray test as well. Just spray the jacket and if the water does not bead up and fall off with a shake then it needs a reviving. That translates directly to the Care section below.
Waterproof/Breathable jackets are subject to contamination from body oils and dirt. DWRs can also be degraded from multiple washings and abrasion. Over time your jacket may need to be washed and have the DWR restored. While I always suggest reading the labels on your particular jacket and following the directions, here is a general practice in caring for your jacket.
First, you will want to wash the jacket following the instructions. There are specially made cleaners on the market (Nikwax, Grangers, etc...) that are made specifically for technical garments. To revive a DWR that has lost some luster it is important to add heat. Heat draws the DWR finish back to the surface of the garment. To apply heat some manufacturers suggest using a steam iron on a low setting. It is a bit tricky so a towel in between the iron and jacket is suggested. Other manufacturers suggest throwing the jacket in the dryer for 15 minutes on medium setting. Make sure to remove the jacket as soon as it is finished in case the inside of the dryer remains hot.
In some cases, you may need to reapply the DWR treatment but this is less common than you think. A durable water repellant finish is just that durable. If you do need to reapply a DWR finish, you can use a spray on method or wash in method. These are available from companies such as Nikwax, Grangers, ReviveX and Sportwash. Just follow the instructions on the bottle.
Hoods are made differently for different applications. Higher volume hoods are great for fitting over skiing or climbing helmets. These are often found on 3-Layer jackets. Smaller hoods are more common on 2-Layer and 2.5 Layer jackets but crossover always occurs. Another thing to be on the lookout for is stashed away or zip-off hoods. More recently hoodless waterproof/breathable jackets have also become more common for high energy activities.
The fastest way to evaporate off sweat will always be direct air exposure. The largest vent on a jacket will be the front zipper but many manufacturers are now making mesh backed pockets, torso vents, and pit-zips (armpit zippers) to allow more venting. While these vents do allow more airflow, they also add weight to the jacket.
Chin guards are normally a strip of fabric between the front zipper and the user’s chin that is commonly lined with a soft polyester material. This is done for comfort reasons as the zipper can cause irritation for some users.
Zippers are not waterproof so many manufacturers add storm flaps over the zippers to protect them from water getting in. There is often and flap of fabric behind the zipper to block wind from getting through as well. These features are nice but do add some weight.
Water-tight zippers are zippers that are installed with the fabric's flaps on the outside. These flaps are then covered with a coating to protect them from water getting through. They are not truly waterproof, so they can only be called water-resistant. The drawback to these zippers is they are slightly more difficult to operate.
Pocket location and number can make a big difference on a jacket. A lot of thought goes into this design. Pockets are thought out for weight, usefulness, and location. For example, you may have a jacket with higher-up pockets, so they can be used when wearing a backpack hipbelt.
Just like other garment jackets come in several different fits. When sizing a jacket think if you need it to be a slimmer cut or have room for layers underneath. Other fit features are articulated sleeves and gusseted underarms. These features add to the comfort and mobility of the jacket. Another important fit aspect is the length of the jacket. Whether you want it to sit on your waist or hips. Many jackets also have a drop tail hem which sits a bit lower in the back.
Not all manufacturers stitch their jacket (some laminate their seams). The stitching can make a big difference in the quality of the jacket. Whether the stitches are straight or not and how many per inch. The more stitches per inch generally mean a better made jacket.
Drawcords & Velcro Closures
Drawcords and Velcro closures are great for adjusting fit and airflow through the jacket. Commonly found on the bottom hem, wrist cuffs, and hood; these are essential at making the jacket fit comfortably.