Hydrostatic Head is a measurement of the amount of pressure that water exerts on a fabric. It's an important factor to consider when choosing any outdoor product, especially tents. A good hydrostatic head rating will keep you dry and comfortable outside in all types of weather conditions. Inflatable tent reviews often mention it, so in this article we'll answer questions like: What does hydrostatic head mean on a tent? What's a good hydrostatic head? Is 5000 hydrostatic head good? We'll go into detail about the benefits of higher quality fabrics with better ratings for your next camping trip or nature hike!
Simply, hydrostatic head means the amount of pressure that water exerts when it is pushing down on a fabric. It's measured by the height of a column of water in millimeters, and this is represented by a number. For example, a tent with hydrostatic head of 5000mm will repel water to the height of five meters before it soaks through. The industry standard for good hydrostatic head ratings is 5000mm to 6000mm.
A hydrostatic head rating (HH) refers to the height of fluid that can be repelled before it soaks through the surface. Different products are likely to have different ratings depending on the conditions they'll be used in. The ability to resist light showers is less demanding than resistance to driving wind, heavy rain, or even more extreme conditions.
The surface tension of water provides some resistance to penetration for the fabric but ultimately pressure will prevail.
The benefits of a fabric with a high hydrostatic head rating are a durable yet lightweight construction that offers resistance to wind and rain while being breathable and water resistant.
Hydrostatic Head Ratings
In general, the higher a fabric's hydrostatic head rating is, the more water resistant it will be. Fabric with high ratings should keep you dry even in wet and humid weather. You should look out for hydrostatic head ratings of 5000mm or higher when looking for materials to be used in the great outdoors, such as tents, jackets, and trousers.
Manufacturers will apply a hydrostatic head test to their products, which involves measuring them by water being sprayed on the fabric while it is stretched. They use a machine to measure water flow by observing how much liquid drips from the fabric after a certain amount of time. Measuring in this way provides a good indication of how quickly water will flow off the fabric when more pressure is applied.
The AATCC 22 protocol is an example of a spray test. A small column of water is placed on the fabric by spraying onto it, and a measuring device will measure how much water leaks off the surface in millimeters per minute.
Hydrostatic head ratings are measured in millimeters: The hydrostatic head rating of a product will be written as 'Xmm' (where X is the height of the water). For example, if a company says their tent has 8000mm hydrostatic head, it means that the water column will get to an altitude of nearly three meters before soaking through.
Fabric Quality & Hydrostatic Head Rating
The level of waterproofing provided by your garment is largely determined by the hydrostatic head rating of its fabric. For example, a jacket with an 8000mm hydrostatic head is going to be more waterproof than one that has 5000mm.
Fabrics used for outdoor equipment such as tents and jackets will often have a hydrostatic head rating between 5000-8000mm.
Different ratings are suitable for different environmental conditions. For example:
- 3000mm is fine for light rain and wind
- 4000mm is suitable for heavy rain
- 8000mm will protect against heavy winds in addition to high levels of precipitation.
Benefits of High Hydrostatic Head Fabrics
A high quality fabric with good hydrophobic properties can help you keep dry in wet and humid weather. It also means your clothes are less likely to stick when out on the trail or hiking through mud - making it easier for you to get dressed quickly at the end of each day's activities! This great resistance also makes these fabrics suitable in higher humidity environments (they're great for stopping condensation in a tent), or where rain conditions are consistently wet.
A fabric with a high hydrostatic head rating will also be more durable, meaning you'll need to replace it less often and can use it in harsher environments without fear of tearing or ripping. Water penetrates fabric and can be trapped inside, where it will cause damage.
What Does Hydrostatic Head Mean on a Tent?
When it comes to tents, the tent material should have at least 5000mm of hydrostatic head water resistance to ensure you'll stay dry inside your shelter. A higher rating will of course be better.
Key items of the tent construction, such as zips and seams, also require hydrostatic head testing because they are vulnerable to water; They are applied to the edges of fabrics or holes in fabric. These points of potential weakness will allow water to penetrate the tent fabric and cause it rot, not to mention letting you get wet.
As a result, you should be looking at more than just the HH rating of the tent waterproofing. Design factors such as the strength of the seam sealers, quality of the stitching, and the zipper construction are just as important.
Waterproofing a tent is an art and it takes years of experience to master all the variables that can affect water-resistance - although learning the best tent waterproofing methods is well worth it for the regular camper..
The best way to know what you're getting is to read the manufacturers warranty, which will cover different hydrostatic head ratings.
A good HH rating on your tent material means that water won't be able to penetrate it. Tents and their parts will need replacing more often if they don't have the required resistance.
The use of high hydrostatic head fabric for tents doesn't just provide protection from outside elements, it also keeps you dry inside. No one needs a leak in their camping life!
Tents made of canvas often have an HH rating of around 3000-4000mm. This is not enough to provide total protection when there is higher water pressure applied, so canvas tents are best used for short time periods or warmer, dryer, weather.
Fabric with a hydrostatic head rating of 5000mm or higher is much more expensive, but the benefits are worth it.
Outerwear, like jackets and trousers should be made from high-quality waterproof fabric with a higher HH score. A good quality jacket should be able to withstand the wind and rain while still being breathable. Waterproof garments usually have an HH rating of 5000mm or higher.
It's especially important that your jacket is waterproof because it will come in contact with your skin and you need to be dry if you're going to be outdoors for any length of time. For warmth and comfort during colder conditions such as when it's likely to snow, you will want a fleece layer underneath your jacket. This should help you stay warm for a while if the waterproofing starts to fail.
Hopefully that gives you a good idea of what a hydrostatic head rating is, and how it applies to the materials that are part of your outdoor equipment. Remember:
- Materials with a higher hydrostatic head rating will keep you warmer and more comfortable in all types of weather conditions.
- Read the manufacturer's warranty to see how long they will stand behind their products.
- Check the other components of your equipment's design to ensure that it's not just the fabric that's waterproof.
- Don't forget: always have a backup plan in case you get caught out with bad weather, and most importantly - enjoy your time outdoors!