Waterproofness 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 it's not overly complex, a few technical explanations are needed to shed light on these concepts and help you select the right garment for your needs.
The waterproofness of a garment
The waterproofness 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 effectiveness of a fabric's waterproofing, the following method is used.
The fabric is placed under a column of water and the height at which the first drops penetrate the fabric is determined. The greater the water height required, the more waterproof the fabric.
The unit used to measure the waterproofness of a fabric is the Schmerber.
One Schmerber therefore corresponds to a water column of 1 mm. A garment with a waterproofness rating of 10,000 Schmerber can withstand a water column of 10,000 mm before letting water through — that's 10 metres of water! It is generally considered that a garment is fully waterproof from 20,000 Schmerber, but a result of 10,000 Schmerber is already a sign of highly effective waterproofing.
You'll readily understand that waterproofness is essential in all situations involving rain, snow or wet environments. Waterproofness is also a guarantee of wind resistance, which also protects against wind chill.
To help you choose a jacket, check out our top picks of best waterproof jackets for hiking and mountaineering. Also browse 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 allow water vapour to escape. With good breathability, a fabric significantly limits the build-up of condensed water vapour inside the garment. Water vapour inside a garment is essentially caused by perspiration and the temperature difference with the humid air that enters the garment.
Depending on clothing and environment, our body at rest releases around 0.06 litres of water per hour. During lightweight effort, this quickly rises to 0.5 litres per hour. During intense effort, one litre or more.
To protect the body against excessive cooling or overheating, the permeability of a material to water vapour is extremely important for the rapid evacuation of moisture.
A fabric with good breathability limits the condensation of water vapour inside the garment. It therefore facilitates the evacuation of perspiration and keeps the body dry.
Good breathability therefore facilitates the evacuation of perspiration and keeps the body and clothing dry. As a result, you'll feel more comfortable and less cold. Indeed, damp skin cools down faster and quickly 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 corresponds to the moisture vapour transmission rate. It simply calculates the quantity of water (in vapour form) that the fabric allows to pass through in 24 hours.
The higher this figure, the better the breathability of the fabric.
MVTR is expressed in gr/m²/24h: that is, the quantity of water vapour evacuated through a surface of 1 m² of fabric in one day.
A value of 30,000 gr/m²/24h is considered a sign of an extremely breathable garment, and 20,000 gr/m²/24h indicates very good breathability. At 10,000, a garment is considered breathable, and poorly breathable if the result is only 5,000 gr/m²/24h.
Waterproofness and breathability in garments: 2 key characteristics together
Combining both qualities in a single garment is a real challenge. That's why research is essential to develop ever more sophisticated membranes and cutting-edge technical methods.
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 getting in the other way. It is this delicate balance that is achieved with the latest membranes to offer you ever more comfortable technical garments.
Also read our article on the care of waterproof garments.
