By Ella Brown
Reading time: 4 minutes
You wouldn't necessarily think that your favorite waterproof jacket isn't actually completely waterproof. In fact, if it were completely waterproof, it probably wouldn't be your favorite jacket. So how is it possible that your favorite waterproof jacket keeps you totally dry, but apparently isn't completely waterproof? Breathability.
What is breathability?
Breathability is a fabric's ability to allow warm water vapor and persperation (sweat) that your body evaporates to escape to the outside.
The breathability of a waterproof material is crucial to the level of waterproofness of the material because without breathability, the material wouldn't be actually be waterproof. Since waterproofness is measured based on how dry the material keeps you, a 100% waterproof garment (such as a rubber raincoat) wouldn't keep you dry the second you start to sweat. Breathability helps excess water inside the material escape.
Breathability is also effected by the design of the garmet/product, not only the breathable fabric. If you have a rain jacket with zippers under the armpits and small holes to promote airation, that can open if you want more air, it is automatically a more breathable design than a jacket without those conceptual design additions.
How does breathability work?
A breathable waterproof fabric is made out of a 2, 2.5, or 3-layers of fabric sandwiched together.
The outermost layer (the colorful one that you see) is called the face layer. The face layer – usually nylon or polyester – is treated with a thin layer of DWR (Durable Water Treatment) which reduces the surface tension of the fabric, forcing the water droplets to bead and roll off instead of seeping into the fabric. DWR treatments are made of a chemical called Polytetrafluoroethylene (PTFE ) that is rubbed into the fabric to ensure that all the fibers are coated. The DWR treated face layer also ensures breathability because it still allows for the tiny water vapor particles to escape from the inside, leaving the bigger water dropples on the outside.
The second – or middle layer – is a tightly woven waterproof membrane with billions of tiny pores that acts as an impermeable layer while simultaneuously allowing the ventilation of bodily water vapors and perspiration.
The third layer is an optional layer called a backer fabric. The addition of a backer fabric is usually made of gives the waterproof material a more comfortable skin-to-skin feel and also protects the membrane from body oils and perspiration. However, the addition of a backer fabric does make the waterproof material have a slightly heavier feel. Waterproof garmets that have the addition of a third layer are especially good for cooler climates as it also gives an extra layer of breatheable insulation.
What is the link between waterproofness and breathability?
Say you have a rubber raincoat that is 100% waterproof. If you are standing still outside in a rainstorm, the rubber raincoat will do its job and keep the water from seeping from the outside to the inside of the coat. However, the second you start to sweat, the raincoat will no longer be doing its job if there isn't a way for the water on the inside of the coat escape. Without breathability, you will be wet on the inside of your coat, which is never fun.
If you have a waterproof raincoat made out of breathable material such as GORE-TEX, Dermizax, Polartec Neo Shell, or Sympatx, you could exert energy in the rain or snow and stay dry at the same time. GORE-TEX is considered to be the best waterproof material on the market currently becaise of how breathable and impermeable it is.
If you are one that tends to bike or walk in the rain while wearing a backpack, it's important to wear a higher-quality waterproof jacket if you intend to stay dry for longer periods of time. If you wear a backpack over your rain jacket, the pressure from the backpack will eventually force the material to leak over time. Higher-quality materials will be more durable against pressure and degradation.
Learn more about waterproof materials here.
How is breathability measured?
Like waterproof ratings, breathability ratings are measured by the clothing company or fabric brand either in-house or at a lab.
A common breathability scale that is used by many popular brands is the Thermal Evaporative Resistance (RET) test. The RET test measures the fabric's ability to allow water vapor to pass through and escape the layers of the material. The RET test is also commonly paired with the EN ISO 811 waterproof test to determine the overall durability and impermeability of the garmet.
The RET test is scored on a numerical index. The lower the score, the more breathable the fabric, is and the higher the score, the less breathable it is.
|RET score range||Breathability level description|
|RET 0 - 6||Extremely breathable and comfortable for physical exercise|
|RET 6 - 12||Very breathable and comfortable for limited physical exercise|
|RET 12 - 20||Moderately breathable but not suited for physical exercise|
|RET 20 - 40||Not very breathable and should not be worn for physical exercise|
|RET > 40||Not breathable|
However, breathability ratings are not currently standardized and most of the tests being done don't necessarily reflect the wear and tear that your garmet may see on a day-to-day basis.