Hydrostatic head what is

An open-ended laboratory test tube is placed on top of the fabric and filled with water. As the water level rises, the pressure on the fabric increases correspondingly. The point at which the fabric begins to allow water to seep through is what is used to determine its hydrostatic head, which is given in millimeters.

For example: if the fabric begins to leak with 10,mm of water pressure, then its HH is 10,mm. Prone to leakage after extended exposure to moderate rainfall. As such, a higher HH in the region of 3,mm and upwards is required to ensure reliable waterproofing. In all but a few cases, however, jackets marketed as out-and-out shell layers boast far higher figures. The following guidelines offer an idea of how these figures translate into performance in the field:.

On the downside, 30,mm-rated fabrics tend to sacrifice breathability and this degree of waterproofing is considered overkill by many other garment manufacturers. Your browser's Javascript functionality is turned off. Please turn it on so that you can experience the full capabilities of this site. Your browser currently is not set to accept Cookies. Please turn it on or check if you have another program set to block cookies.

You could learn the difference between a mm and a 5,mm Hydrostatic Head rating through firsthand experience like this guy is, or just keep reading here and find out the much easier way….

This is done using an open-ended laboratory test tube, which is placed on top of the fabric and then filled with water. The higher the hydrostatic head, the more waterproof the fabric will be.

This largely depends on who you ask — or, rather, what part of the globe they hail from. However, some countries prefer to do it their own way. In Germany, for instance, fabrics are considered waterproof if they have an HH of 1, mm or more.

In the UK, the Ministry of Defence sets the bar low at a mere mm. While some waterproof clothing items and tents are so impermeable that they could almost moonlight as space suits or submarines, others are only equipped to save you a soaking in light and short-lived rain showers. It takes far more to make a great waterproof garment or tent than a stellar hydrostatic head rating alone.

In tents, waterproofing will also we determined by the design of the tent, the type of flooring, and whether or not it has sealed seams, storm flaps, awnings, skirts, and waterproof treatments.

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