The breathable Waterproof ; Part1


I have designed Jackets for 25 years and I get some questions always still get asked, is it breathable, is it waterproof. The simple answer will most likely be yes! But then there is an expectation to hear a large numbers from a test that most do not understand or care to understand. As long as the number appears to indicate the fabric has a performance.

As a designer role is to question and I ask slightly different questions. Why does it work? and does it suit the function? Here is some information why you can not take waterproof figures as a true measurable reality.

Waterproof Fabrics

The European Standard for a fabric to be considered and classed as waterproof is a hydro-static head rating of 1,500mm. The international ISO 811 standard is that fabric must be tested up to 1000 millibar (i.e., 1 bar) – which is equivalent to a hydro-static head of 10 197 mm water – equivalent to 14.5 psi

All seams must be factory sealed or taped on the inside of the fabric (or water will penetrate the stitch holes) although pockets are not necessarily required to be waterproof given the fashion for mesh linings.  Many waterproof fabrics also have a durable water repellent (DWR) outer coating.

Although a hard rain would likely generate a maximum of about 2 PSI / (equiv. to c. 1400mm hydrostatic head pressure), fabrics can be subjected to far greater pressures during normal outdoor life (e.g. when kneeling (which generates a pressure of c. 18 psi  / sitting (7 psi in someone weighing c. 170 lbs) / from rucksack strap movement (c. 30 psi) etc).  In most instances, however, a hydrostatic head of c. 10,000mm is more than sufficient for outdoor activities so long as the garment has been designed appropriately.

Waterproof design, minimum requirement to be waterproof.

  1. Made from a waterproof fabric

  2. Seam sealed with a tape or (in Ventile jackets uses felled seams)

  3. Paneled in a way that seams are away from pressure points (like shoulders, elbow and seat)

  4. Storm flaps applied to openings and pockets.

  5. Water, wind, and snow effects considered for the protection of the wearer.

Whilst most branded fabric companies quality check the waterproofness of the designs of the garment manufacturers using their technology, rain room tests have shown instances when garments made from a fabric waterproof to less than 1000 mb are more waterproof than garments made of a fabric with a hydrostatic head exceeding 20 000mm due to the design of zips, hoods etc.  In other words, if you get wet in a waterproof garment / shoe this could as easily be due to the garment manufacturer’s design as it could be to a defect in the fabric (or, most commonly, to a lack of fabric care).  This is why the first port of call, on a return, is the garment manufacturer.

Having said this, do not fall for the trap of presuming that the higher the waterproof number, the better the fabric / jacket. By this logic, the best rain jacket would be a sheet of totally waterproof pure rubber / plastic – but who wants to walk around sweating in such a non-breathable material?

Similarly, when some brands quotes (shall remain nameless) , for instance, numbers like the 250,000 psi, this is almost completely irrelevant in real world usage – especially given that your seams will have started to leak once subjected to pressures greater than 2 psi!

Beware, rather, of the fact that some fabrics achieve high waterproof ratings at the expense of breathability, and that when this is the case, you risk becoming as wet from your own sweat as you ever could have been from the rain.

When you consider that the average person sweats 200ml of sweat an hour just walking down town to collect the paper, and 600ml an hour when running, (the equivalent of 3/4 of a Nalgene bottle! Or just over 1 pint) you can start to see why this is important.  You wouldn’t feel very dry inside a fully waterproof jacket if someone poured a bottle of water down your neck!

If water vapour cannot escape from the body’s surface, through the fabric layers to the environment, it has to condense in either the cooler outer layers of the clothing system or on the inner surface of the shell fabric – neither of which are optimal for the user.  The accumulated water, trapped inside the fabric, next to the wearer, leaves them feeling first clammy, then damp from sweat build-up, and then, ultimately, as wet as if the fabric wasn’t waterproof at all!

The real trick, therefore, for fabric brands is to find the “sweet spot” that achieves a level of real world waterproofness (not just “water resistance”) without sacrificing breathability.  Similarly, when choosing a garment, choose both a fabric with the functional potential to provide the real-world waterproofness that you require at the level of breathability that you will need for your intended activity / end use activity.

DWR: Durable Water Repellency

DWR (durable water repellency) applications of hydrophobic coatings are made to the face fabric of WP / B fabrics during production.  Some companies apply this coat pre lamination and some, afterwards.  Water repellency is a fabric’s ability to make water “bead” and roll-off, rather than soaking into them and serve as a first barrier to penetration of the fabric by external water.

When a fabric’s DWR layer is robust, water simply beads off its surface.  However, the DWR finish degrades over time and will occasionally need to be replenished. You will be able to tell when this water repellency has degraded because water will cease to bead up on the fabric. A solid water layer will form on the top of the fabric and then start to soak into it.  Once fully saturated on the outside, the jacket will start to feel wet on the inside even if there is no transfer of water inwards across the membrane since the movement of perspiration will have been blocked and the user will become wet from the inside out.

The quality of a DWR application is more to do with the choice of face fabric (since some fabric structures accept the same chemical coatings better than others) than it is to do with the WP / B brand.  In other words, if two different brands chose to use same face fabric, its DWR performance would be influence by this more than by the choice of e.g., Gore / eVent / Porelle as the integral WP / B technology.

DWR performance is a vital component in the fabric’s overall performance and 9 out of 10 WP/B jackets returned are to do with DWR problems on the face fabric (primarily due to a lack of correct maintenance).  DWR coatings can and do wear or wash-off (they can be renewed or re-activated) whereas waterproof inner coatings or membranes will to a greater or lesser degree last the lifetime of the garment.

Fabric breathability tends to drop over time.  Either the DWR application wears off, allowing the face fabric to saturate (which therefore blocks the movement of sweat and leaves the wearer feeling like the jacket is no longer waterproof even if the membrane is intact), or the membrane becomes so clogged with dirt (if not washed well) that no moisture movement can occur. In both instances, a degree of breathability can be returned through proper care of the garment in question. Most manufacturers provide clear wash care guidelines which should be strictly followed for maximum performance and longevity of the garment.

DWR repellency can be re-invigorated by using sprays or wash-in products.

Common brands of DWR finishes include which have PFC:

  • ReviveX (fluoropolymer base)
  • Scotchguard (fluoropolymer base)
  • Tectron (fluoropolymer base)

Common brands of DWR finishes with alternative bases which free from PFC:

  • Kiwi Camp Dry (silicone base)
  • Nikwax (patented wax-elastomer base)
  • Granger’s (fluoropolymer base)

In the image shown, the top part is ironed after washing and the water repellent is working by making the water bead up. Bottom part is not ironed after washing and becomes soaked.

Despite the name, durable water repellent finishes tend to wear off and may need to be re-applied from time to time. The application method will probably make a big difference in the DWR you choose to use. Most fabric treatments are applied either by adding to a regular wash cycle in a washing machine, or by spraying.

Fluoropolymer-type repellents tend to lose their properties when washing.  Such garments need tumble drying in medium heat or ironing to restore the repellency.

Breathability Fabric Definition

A completely waterproof fabric that does not allow passage of the moisture-laden vapour generated by the body during exercise will quickly saturate the wearer as moisture condenses inside.  High levels of hard shell, softshell and wind shirt fabric breathability are key to all day comfort and the best outerwear fabrics have both high water resistance and high breathability.

Breathability is sometimes referred to as water vapor transmission rate (MVTR) – in other words, it is the ability of a fabric to transport water vapor from one side of the fabric to the other.   Nominally, the greater the MVTR, the faster water vapor moves from the inside of your garment to the outside, and the less moisture you’ll accumulate while exercising.

Waterproof/breathable fabrics are sometimes defined as fabrics that will withstand (have a hydrostatic head of) over 1000 millimetres of water (9.8 kPa) pressure without leaking, whilst allowing water vapour to pass through. Their most common use is in outdoor sports clothing and single wall tents, because of their ability to allow sweat to evaporate while remaining impervious to rain.

Waterproof Garments MVTR’s of anywhere from 5 – 10,000gm/m2/24 and above are considered acceptable,  but brands will find many ways to arrive at these figures that direct comparisons of figures quoted by different manufacturers are impossible.  Different tests reflect different parameters of breathability.  Unlike for waterproofness, there is no industry standard breathability test and the ratings tend to be very subjective, with little direct relevance to real world scenarios.

In addition, the breathability of most waterproof/breathable fabrics is very dependent on conditions. Cold weather can affect the dew point (the point at which condensation occurs), as can high humidity and most PU-containing fabrics become effectively worthless in tropical climates since they are dependent upon a high internal vs external moisture pressure to push the water molecules through their system.

For all of these reasons, fabric suppliers tend to shop around for a test that shows their product to its best advantage and it becomes almost impossible for retail staff, let alone the consumer, to compare and contrast the conflicting information provided.

Add to this equation the fact that some fairly standard test methodologies rely on the inside of the fabric being wet before a reading is taken (not an ideal outdoor scenario), that garment design plays a huge role in whether the fabric meets its own potential w.r.t. comparative lab test results (i.e. that the lab numbers do not always correlate to field performance if, for instance, the cut prevents air circulation / a great deal of low breathability seam tape is used on the garment etc.) and the fact that fabrics with hydrophilic components change their properties under different humidity conditions – and it is no wonder that most people are confused by this subject!

In general, however, the more active the user (or the more likely to sweat, irrespective of exertion levels), the more critical is the breathability rating of the fabric and both fabric breathability and garment construction should be considered carefully when purchasing outdoor products since trapped sweat can not only prove uncomfortable but can also be dangerous.

Breathability Tests

Breathability in particular, the controlled and generally static conditions in a lab environment are not scalable to assessing the performance of a garment in the field.  Even lab tests incorporating moving and sweating mannequins clothed with realistic apparel systems and subjected to blowing wind, fall short of predicting actual field performance on human subjects.   Although physiological testing on human subjects sounds feasible, it is actually extremely complicated since then variables such as individual metabolic variability, individual perspiration level, personal fitness, activity level, what garments are worn under the shell, shell venting characteristics (e.g. pit-zips), garment fit, whether or not the shell “pumps” air (which is governed by fit, ventilation, and body motion), the type of activity performed, wind speed and direction, outside temperature, precipitation levels, etc must all be taken into consideration. The list could go on!

Breathability can be measured in the lab in over 30 different ways.  Some tests are conducted with the fabric saturated on the inside. Whilst others fabrics mimic more normal real world scenarios and start with the fabric dry on the inside.  Since the method of determination of MVTR numbers are rarely provided. It is only possible to compare the breathability of fabrics within brands rather than across brands.  There may be some value in comparing the relative MVTRs from 10–15 different fabrics from the same fabric company. You could not usefully compare these to the MVTR numbers promulgated by other fabric technologies from other sources.  As a step towards standardisation, some people are pushing for a combined rating from both testing methodologies to be provided.