Water column in rain jackets: What do the values mean?

When the sky darkens and the first drops fall, your outdoor gear shows what it's really made of. The water column in rain jackets is the crucial metric that determines whether you'll stay dry or get soaked during your time in nature. But what is a good water column in rain jackets really – and which value is right for your next adventure? In this guide, you'll learn what matters, how it's measured, and which values you need for different activities.

What does the water column mean on a rain jacket?

The water column of a rain jacket is a standardized unit of measurement that indicates how waterproof a material actually is. Put simply: the higher the water column, the better your jacket protects you from moisture. It's measured in millimeters (mm) – the value describes how much water pressure the fabric can withstand before the first drops seep through.

For comparison: tents, pants, and backpacks are also rated using the same principle. If you spend a lot of time outdoors, you should definitely know this metric, as it makes the difference between a pleasant tour and an uncomfortable wet experience.

• Hikers benefit from high values on longer multi-day tours.
• Cyclists need protection that holds up against wind and splash water.
• Mountaineers depend on maximum water resistance in extreme weather conditions.

Especially on cold or wet tours, the right base layer also matters for your comfort. An breathable Merino functional underwear as a base layer complements a high-quality rain jacket perfectly.

How is the water column in rain jackets measured?

The water column is measured according to a standardized procedure, usually following the standard DIN EN 20811. The outer material of the jacket is stretched under a water cylinder and gradually subjected to water pressure. The pressure increases until exactly three water droplets reach the inside of the material. The measured value is then converted to millimeters of water column.

As a rule of thumb:

• 0.1 bar pressure = 1,000 mm water column
• 0.2 bar pressure = 2,000 mm water column
• 1.0 bar pressure = 10,000 mm water column

According to European standards, a material can officially be called "waterproof" starting from a water column of 1,500 mm. In practice, however, this is far from sufficient to reliably keep you dry during heavy rain or over longer periods.

What is a good water column in rain jackets for different activities?

The question of what a good water column in rain jackets is depends heavily on the intended use. Not every activity requires high-tech materials, but with intensive outdoor use, you shouldn't compromise on protection.

• 1,500 – 4,000 mm: Protection against light drizzle for short periods – ideal for city and everyday use.
• 5,000 mm: Withstands brief showers but quickly reaches its limits.
• 10,000 mm: Solid protection for hiking and cycling in heavier rain.
• 15,000 – 20,000 mm: Recommended for mountain tours, trekking, and intensive outdoor activities.
• Over 20,000 mm: Professional level for extreme conditions, high-altitude climbing, and expeditions.

Example: Is a rain jacket with 5,000 mm water column really waterproof? Yes, in light drizzle – but as soon as you encounter a proper downpour or carry your backpack on your shoulders for a while, the additional pressure becomes a problem. First you'll feel moisture on your arms, then the rain penetrates the rest of the material.

For autumn and winter tours, a water column of at least 10,000 mm is therefore recommended, preferably 15,000 mm or more. If you're hiking with an ultralight 40-liter backpack for winter tours, the weight presses down on the material – one more reason not to skimp on protection.

What else to look for in your rain jacket besides water column

Water column alone doesn't make a perfect rain jacket. To truly stay dry, several other factors play an important role:

• Breathability: High water vapor permeability (MVTR) prevents you from getting wet from the inside.
• Sealed seams: Even the best material is useless if water enters through the seams.
• Durable zippers: Waterproof or covered zippers prevent moisture from seeping in.
• Water repellent coating (DWR): The outer coating ensures water beads off and the material doesn't become waterlogged.
• Fit and ventilation: Adjustable hood, cuffs, and pit zips provide a comfortable climate.

Accessories also make the difference for dry tours: With the right trekking poles for cold and wet conditions, you'll stay stable on slippery terrain. And after a rainy day, an ultralight sleeping pad provides comfortable sleep in your tent.

Frequently asked questions about water column in rain jackets

At what water column is a rain jacket truly waterproof?

Officially, a material is considered waterproof from 1,500 mm. For real outdoor use, however, you should choose at least 10,000 mm, or 15,000 to 20,000 mm for longer tours and heavy backpacks.

Does the water column change over time?

Yes, through abrasion, washing, and UV exposure, the water column can decrease over time. Regular impregnation with DWR products refreshes the protection and significantly extends the life of your jacket.

Is a higher water column always better?

Not necessarily. A very high water column often means stiffer material and lower breathability. If you mostly hike in moderate weather, you'll usually be more comfortable with 10,000–15,000 mm than with expedition-grade values.