What is a membrane?
The main task of waterproof jackets (or pants, shoes...) is to protect us from the elements. They need to protect us from water and wind, but at the same time they need to be comfortable to wear. A major influence on comfort is the breathability of the jacket. The fact that a jacket is breathable (or "breathable") means that it allows moisture to be transferred out of the jacket. There are many waterproof garments that will protect you from water and wind, but only the best ones will also ensure that sweat does not accumulate under the garment. But how do they do this?
Membrane
The membrane is what makes clothes waterproof. The membrane is usually made of polytetrafluoroethylene (PTFE) or polyurethane (PU). The latter are made into thin fabrics that have thousands of microscopic holes that are too small to let water droplets through, but still large enough to let steam through.
But we don't have to use the membrane by itself. The membrane is always bonded with another fabric. We know 3 types of waterproof fabric constructions: 2-layer (2Layer), 2.5-layer (2.5Layer) and 3-layer (3Layer)
2L (layer):
2-layer fabric means that the outer fabric is bonded to a membrane. This construction is used in garments that have an additional inner fabric. This inner fabric is not bonded to the membrane, but protects it from particles that can damage it (e.g. oils and salt).
2L garments are usually looser and heavier than other constructions. However, the most products on the market are made from 2L membranes, as they are the easiest and cheapest to produce.
2.5L (layer):
Very similar construction to 2L, the only difference is that the inside of the membrane is protected by an additional coating. This means there is no need for an inner fabric, making the garment lighter and thinner.
This type of construction is the lightest and folds the smallest, while also being affordable.
3L (layer):
A 3-layer fabric is a membrane bonded to an outer and inner fabric. Because it is protected from both sides, it will last longer and offer better protection. The 3L membrane is the most expensive option, but due to its durability, it is best suited for prolonged exposure to the elements and extreme conditions.
DRW - (Durable Water Repellent):
Waterproof fabrics are usually treated with a DRW coating, which protects the fabric and increases its water resistance. It is an excellent protection for clothing, as it also extends its lifespan, but it wears off over time. It is possible to reapply the protection, which is highly recommended (e.g. Stom Eco+ Proofer ).
Waterproofing of the membrane:
The waterproofness of a membrane is measured by the water column (from 1,000mm to 35,000+mm). The higher the water column value, the more waterproof the fabric.
5,000 mm – 9,000 mm - the fabric is considered waterproof but will only protect you from light rain and dry snow. In heavier rain the fabric will get soaked. Recommended for urban use and short-term exposure to rain or dry snow.
10,000mm – 19,000mm – The fabric holds water well. It will not soak through in rain or snow, but will let water through if water pressure occurs (when exposed to heavy rain with strong winds or when squatting in the snow for a long time). A waterproof jacket of this rating is suitable for most hikers.
20,000 mm – 30,000 mm + - The fabric does not let water through even in the heaviest downpour or wet snow. Suitable for winter mountaineering ascents, prolonged exposure to heavy rain and for anyone who wants the best protection from the elements in unpredictable weather conditions.
Membrane air permeability:
The breathability of the membrane is measured using the MVTR (moisture vapor transmission rate) test. It measures how much vapor passes through the fabric within 24 hours. The result is expressed in g/m². The higher the value, the better the fabric breathes.
But the breathability of waterproof fabric is affected by many factors, such as temperature, humidity, cleanliness of the fabric, quality of the DWR coating... Therefore, proper maintenance and cleaning are necessary for best results.
5,000 g/m² – 9,000 g/m² - a jacket in this breathability range is suitable for alpine skiing, urban use or camping. However, condensation would start to form during activities such as hiking, climbing and running.
10,000 g/m² – 15,000 g/m² - the jacket is suitable for most moderate activities, e.g.: climbing, ski touring, hiking...
1 6,000 g/m² – 20,000 g/m² + - the jacket is suitable for activities where you sweat a lot, e.g.: running, off-road running, snowshoeing, cycling , trekking in warmer climates...