10,000mm Water Column: What This Number Really Means

If you've researched waterproof jackets, you've probably seen the "water column" spec measured in millimeters. But what does that number actually mean in practice?

The water column is an industry-standard test: it measures how many millimeters of water a fabric can withstand before it starts leaking, using a tube of water positioned over the material. The higher the number, the more water-resistant the fabric is under pressure.

How to read it:

Up to 5,000mm: resistant to light rain and drizzle, suitable for everyday urban use.

5,000 to 10,000mm: good for moderate rain and snow, holds up under backpack straps and kneeling on the ground.

Above 10,000mm: the level used in technical jackets for hiking, mountaineering and winter sports, resistant to prolonged heavy rain and intense pressure.

It's worth remembering that waterproofing and breathability go hand in hand: a good technical jacket needs to protect against water without turning into a sauna inside. So alongside the water column, it's also worth checking the breathability rating (measured in g/m2/24h) before deciding which piece to bring on your next adventure.