Waterproofing and breathability are terms frequently used in the descriptions of technical garments such as waterproof jackets. Yet few people truly understand what they mean. While the concepts aren't overly complex, a few technical explanations are needed to shed light on these notions and help you choose the right garment for your needs.
The waterproofing of a garment
The waterproofing of a fabric or membrane is its ability to prevent water from penetrating.
Waterproofing is achieved by bonding a membrane to the fabric or by applying a coating to it. To measure and quantify the waterproofing effectiveness of a fabric, the following method is used.
The fabric is placed under a water column, and the height at which the first drops pass through is measured. The higher the water column needed, the more waterproof the fabric.
The unit used to measure the waterproofing of a fabric is the Schmerber.
One Schmerber equals a water column height of 1 mm. A garment with a waterproofing rating of 10,000 Schmerber can therefore withstand a water column of 10,000 mm — that's 10 metres of water — before letting any through. A garment is generally considered fully waterproof from 20,000 Schmerber, but a result of 10,000 Schmerber already indicates highly effective waterproofing.
Waterproofing is essential in any situation involving rain, snow, or wet environments — that much is clear. It also provides resistance to strong winds, which in turn protects against wind chill.
To help you choose a jacket, check out our pick of the best waterproof hiking and mountaineering jackets. Also explore our collection of technical waterproof trousers to gear up for tough conditions.
The breathability of a garment
Breathability is the ability of a fabric or garment to evacuate water vapour. With good breathability, a fabric significantly limits the build-up of water vapour condensation inside the garment. Water vapour inside a garment is primarily caused by perspiration and the temperature difference with the humid air that enters the garment.
Depending on clothing and environment, the body at rest releases around 0.06 litres of water per hour. During light exercise, this quickly rises to 0.5 litres per hour. During intense effort, it can reach one litre or more.
To protect the body against excessive cooling or overheating, the permeability of a material to water vapour is critically important for the rapid evacuation of moisture.
A fabric with good breathability limits the condensation of water vapour inside the garment. It therefore helps wick away perspiration and keeps the body dry.
Good breathability helps wick away perspiration and keeps both body and clothing dry. As a result, you'll feel more comfortable and less cold. Damp skin loses heat far more quickly and becomes vulnerable, losing its ability to warm up naturally.
MVTR measurement
There are several ways to measure the breathability of a product, but one method is predominantly used by French clothing brands.
The MVTR measurement refers to the moisture vapour transmission rate. It simply calculates the amount of water (in vapour form) that the fabric allows through in 24 hours.
The higher this figure, the better the breathability of the fabric.
MVTR is expressed in g/m²/24h: that is, the amount of water vapour evacuated through 1 m² of fabric in a single day.
A value of 30,000 g/m²/24h is considered a sign of an extremely breathable garment, and 20,000 g/m²/24h indicates very good breathability. At 10,000, a garment is classed as breathable, and poorly breathable if its result is only 5,000 g/m²/24h.
Waterproofing and breathability in garments: 2 key characteristics working together
Combining both qualities in a single garment is no easy feat. That's why research is essential to develop ever more sophisticated membranes and cutting-edge manufacturing techniques.
The membrane (or coating) of a fabric contains millions of microscopic pores per cm². These must be large enough to allow water vapour to escape (perspiration), yet small enough to prevent rain and moisture from penetrating in the other direction. It is this delicate balance that the latest membranes achieve, delivering increasingly comfortable technical garments.
Also check out our article on the care of waterproof garments.
