We often hear that a jacket is waterproof or has a 15,000 mm water column, but… what does this really mean? If you're gearing up for your mountain adventures, understanding the difference between waterproof, water-repellent, and water-resistant is key to making the right choice. In this article, we'll explain what waterproofness is, how it's measured, and what the famous water column implies.
What it means for something to be waterproof
When we say a garment or piece of equipment is waterproof, we're referring to its ability to prevent water from passing through it. In other words, you can be in the rain or in contact with snow for hours without getting wet… provided the garment truly is waterproof.
However, waterproof is not the same as water-resistant or water-repellent. And this is where the confusion comes in.
Difference between waterproof, water-resistant, and water-repellent
- Water-resistant: Offers basic protection. It can withstand light drizzles or splashes, but won't keep you dry in a storm.
- Water-repellent: Has a treatment that makes water bead up and roll off the surface of the garment (the famous DWR), but if the rain persists, it will eventually soak through.
- Waterproof: Completely blocks the passage of water, even in conditions of intense and prolonged rain. This is what you need in the mountains if the weather can be extreme.
So, if you're wondering what water-repellent means, the short answer would be: "it protects you for a while, but don't rely on it in the middle of the mountains."
What factors influence waterproofness
The waterproofness of a garment doesn't depend solely on the fabric used. There are several key elements that contribute to a garment being truly effective at protecting you from water. From sealed seams to specific treatments, as well as design and fit, each of these factors plays a fundamental role.
Sealed seams
A fabric can be waterproof, but if the seams are not sealed, water will find its way in. Heat-sealed seams are key to preventing leaks.
DWR treatment
DWR (Durable Water Repellent) is a coating that makes water bead up and slide off the surface. Although it doesn't make the garment waterproof on its own, it helps keep the outer layer dry and improves breathability.
Garment design and fit
A jacket with a good hood, flaps covering the zippers, and an adequate fit will protect you better than one that lets water in through the cuffs or collar.
Intensive use, with a backpack, etc.
Constant rubbing from a backpack or sitting on a wet rock can compromise waterproofness. Therefore, the use of the garment and its natural wear and tear also influence its waterproofness.
Why do you need waterproof clothing in the mountains?
In the mountains, the weather can change in a matter of minutes. What starts as a sunny day can end with intense rain, fog, or even snow. Being exposed to moisture and wind without adequate protection is not only uncomfortable but can also put your health and safety at risk. A quality waterproof jacket is not an optional accessory: it is as essential as good footwear. It helps you maintain body heat, prevents you from getting wet, and allows you to continue moving forward with confidence, even when the weather gets complicated.
How waterproofness is measured
To determine how waterproof a garment is, there are several tests, but the most common and internationally standard is the water column test. Although other tests may include rain simulations or pressure tests, the water column remains the primary reference for evaluating a garment's ability to resist the passage of water.
What is the water column
The water column measures how much water pressure a material can withstand before it starts to leak. This test is performed by placing a fabric sample at the bottom of a vertical tube filled with water. The measurement obtained is the height of the water (in millimeters) that can be above the fabric before water begins to penetrate it.
Imagine the tube is one meter high (1,000 mm). If the water rises to 5,000 mm above the sample and there are no leaks, that fabric has a resistance equivalent to a 5,000 mm water column.
To put it in context:
- 5,000 mm: Basic resistance. Ideal for urban use or light rain.
- 10,000 mm: Good option for hiking or activities with moderate rain.
- 15,000 - 20,000 mm: Perfect for mountaineering, snow, or very humid climates.
- More than 20,000 mm: Extreme use, such as in alpinism or prolonged expeditions in high humidity or constant rain conditions.
So, when you see a garment labeled "20K water column," it means it has been tested to resist 20,000 mm of water before leaking.
10k, 20k, 30k… What do I need?
The water column gives you a clear idea of water resistance, but the choice of garment depends on the activity you are going to do and the weather conditions you face. Here are some recommendations:
- 5,000 to 10,000 mm: Ideal for urban use or easy routes where light or intermittent rain is the most you can expect. It is also sufficient for short walks where you are exposed to the elements for a short time and can easily take shelter.
- 10,000 to 15,000 mm: This range offers a good balance between protection and comfort. It is suitable for longer hikes where moderate or constant rain may appear and you are likely to be outdoors for several hours.
- 15,000 to 20,000 mm: From this level, the protection is notably superior. It is recommended if you do full-day or multi-day mountain routes, where the weather can change quickly and exposure to rain or snow is prolonged.
- More than 20,000 mm: Designed for severe conditions, torrential rain, constant snow, or activities where you will be many hours without shelter. It is also the best option if you practice winter sports, as contact with snow and cold requires more solid and durable protection.
It is important to note that, although greater water resistance is key to keeping you dry, more is not always better. As waterproofness increases, the breathability of the garment may decrease, which would affect your comfort if you perform high-intensity activities.
Waterproofness or breathability, what is more important?
The answer is not as simple as choosing one or the other; the key is to find the balance. A garment can be extremely waterproof, but if it doesn't allow sweat to escape, you'll end up soaked inside, which could be even more uncomfortable than getting wet in the rain. In the mountains, breathability is as crucial as waterproofness to maintain your body temperature stable and prevent internal moisture accumulation. When choosing your equipment, always look for garments that offer a good combination of both characteristics, thus ensuring external protection and internal comfort.
How to care for your waterproof clothing so it lasts longer
A well-maintained waterproof garment can last for years. But if you don't give it proper maintenance, it will quickly lose its properties.
Here are some basic tips:
- Wash them with specific products, not regular detergent.
- Reactivate the DWR.
- Reapply water-repellent treatment when you see that water no longer beads up.
We recommend reading our article on how to care for your technical clothing if you want more information.
Knowing what waterproofness is and how it is measured is essential to choosing your mountain equipment well. Whether for a weekend getaway or a serious expedition, a good mountain jacket can make the difference between an incredible experience or a day spent in the rain… and cold.
Remember: don't just go by the numbers. Consider the use you will give it, the weather, and, above all, that it fits you well.
