What is the water column?
The water column is a standard which allows comparing different fabrics to their water resistance. In other words, it indicates how long it takes to pass a substance of water.
How is it calculated?
To determine the water column, 10cm² of the respective fabric is clamped under a measuring cylinder (= column). The cylinder is then filled with water step by step. This increases the pressure on the fabric increasingly (by 10mm per second). Now the time is measured until three drops have formed on the back of the fabric.
Example: If, after 10 seconds, three drops of water are seen on the underside of the fabric, it has a water column of 100mm.
And what are the figures now saying?
Fabrics are called as water-repellent or waterproof by their water column. If you are looking for a rain jacket or a tent, you will, of course, look for a waterproof product. But beware! According to the European standard textiles from 800mm water column are called waterproof (class 2) … in heavy rain or longer tours is not much!
For this reason, you should not only trust the term “waterproof”, but you should always look at the water column as well!
Waterproof (class 3) is a fabric with a 1,300mm water column. It is important to note that we only speak of our European standard. In Switzerland, for example, a fabric is only called waterproof with a 4,000mm water column, and other countries can also have different standards.
To get a feeling for what this whole millimeter of water column values means at the end I have here a small example:
When sitting on a wet surface, about 2,000mm water column is built up. (depending on the weight of the person)
The tents are subject to different standards: while tent walls can be classified as waterproof at 1,500mm, the floor must be able to withstand at least 2,000mm.
Are there fabrics that are 100% waterproof?
Sure, there are textiles that never let water pass. In the field of outdoor clothing, however, they are not very popular since an absolute seal is at the expense of breathing activity. This means that you will still get wet because sweat cannot be transported away from the body.
Which water column value do I need?
To mention a concrete number at this point is not so easy. From my research and my own experiences, I would say that good outdoor jackets should have a water column of at least 10,000mm.
The right water column for you personally entirely depends on what you want to do in the rain and what is the load on the fabric. It is important to know whether the fabric has to withstand other stresses, in addition to the water. Such stresses can be, for example, the wind or a heavy backpack. Accordingly, you should pay attention to a higher water column.