How waterproof is your tent? Hydrostatic Head explained.

If you are planning on buying a tent for camping next year (you are, right?) and the tent is made from a polyester-based material, then you will have seen as part of the specification of the tent a ‘Hydrostatic head’ measurement, usually specified in millimeters. The is essentially a measure of how water resistant the fabric of the tent is.

If the specification says your tent has a hydrostatic head of 4000mm this means that the tent fabric could hold a column of water 4000mm tall before the water pressure started to force the water through the fabric.  The higher the number, the more water resistant the tent and the more rain and weather it can withstand before it leaks.

Canvas tents do not normally have a hydrostatic head measurement as the way the canvas fabric becomes waterproof is different. Because canvas is a naturally breathable material and  swells when wet it creates its own seal and with the pitch of the roof water runs off readily.

Of course, the fabric is not the only source of water resistance, it is important also that your tent has good seams, seals and zips as all of these parts of a tent are potential places for water to enter.

How waterproof is your tent? Hydrostatic Head explained.