Hydrostatic head is also called water column and is a measurement of waterproofing – but do not count on the numbers alone!
How is it measured?
To measure the hydrostatic head of a fabric a column of water is pressed against the fabric. The height of the water in the column is slowly increased until the water penetrates the fabric. The height of the water just before the water penetrates is the hydrostatic head measured in mm, like 3000 mm which is actually three meters of water!
A basic compromise
Hydrostatic head is a delicate balance. On one hand you want your tent to be very waterproof – but on the other hand you want high breathability.
If the tent is too waterproof with a very high hydrostatic head water will condensate on the inside and create poor indoor climate – just like sleeping in a plastic bag.
A quick guide to waterproofness
- Hydrostatic head is a measurement of waterproofing
- The higher the number, the more waterproof the fabric
- Balance: a tent should be waterproof yet breathable
- For a flysheet 2000+ mm will endure most European rain in all seasons
- For a groundsheet the general rule is a hydrostatic head of 8000+ mm
Nylon and polyester are both lightweight and durable synthetic fabrics that share many of the same properties, such as easy care and resistance towards wrinkling, stretching, shrinking and abrasion – and both are naturally hydrophobic, which mean they absorb very little water. Both polyester and nylon are easy-care fabrics that can be machine washed and dried, though low heat is recommended. But neither is a better fabric as it depends on needs, purpose and use.