Equipment: What is Hydrostatic Head?

When choosing rain weather equipment (clothes, tent, etc.), the main water resistance indicator you will encounter is the water column. But what exactly does this term mean? The water column is a unit of pressure that gives a volume of water over 1 square cm of matter. It is measured in millimeters per unit area. That is, a 3000mm (or 3m) water column means that this is the maximum pressure that a fabric can withstand a square centimeter without water leaking.



You can imagine it this way - a non-bottomed tube measuring 1 square cm is placed on the fabric. and water begins to pour into it, measuring the height of the water column in millimeters. The maximum height that the water reaches the tube before the fabric begins to leak is its water column. This is how the degree of water resistance is characterized - that is, the higher the water column, the more resistant the matter is.

The water tightness standard for waterproof clothing starts from a 1000mm water column tent. Tents require a 1500mm water pole to withstand light rain for extended periods of time. Specifically, with regard to tents, there are other factors that have an impact, you can read about them in our article “Waterproofing the tent”.

For clothes it should be borne in mind that the higher the water column, the lower the "breathability" of the fabric and, accordingly, the evaporation of sweat is difficult.

The water resistance of the fabric is usually achieved by applying a layer of synthetic material to seal the pores of the fabric. With prolonged use, this layer gradually wears off. However, it can be recovered using various impregnating agents, such as sprays.