You may have come across the term ‘Hydrostatic Head’ when shopping for tents, jackets, or even groundsheets — the term ‘Hydrostatic Head’ is actually a measurement. More specifically, a measurement as to how tall of a water column the fabric can hold before water starts to seep through the material, which essentially refers to how water resistant the material is.
Take for example a polyester tent that has a hydrostatic head of 3000mm. This would mean that it can hold a column of water that is 3000mm tall. Any more and water will start to seep through the material. Hence, the higher the hydrostatic head value of a material, the more water-resistant it is.
So what would be an ideal hydrostatic value for a tent? Well, if having a higher hydrostatic head means higher water resistance, doesn’t that mean that the highest value possible would be the best? In theory, the higher the value the better it definitely will be. However, hydrostatic head values aren’t the only defining factor when it comes to how waterproof your tent will be.
What Is A Sufficient Hydrostatic Value For A Tent?
Typically, most tents come with a hydrostatic head value of 3000mm, and that would be a good gauge of what is enough to withstand rainfall in the UK. To be able to call a material water-resistant, it requires a minimum hydrostatic head value of 1000mm.
Harsher rain and snowy climates will obviously call for tents with higher hydrostatic head values. If you plan to camp where there is snow or frequent heavy showers, we recommend you look for tents with hydrostatic head values of 5000mm up to 10000 mm.
Tents with hydrostatic head values of above 1000mm would be sufficient for regions that are dry and rarely see rainfall. Since most polyester tents have a minimum hydrostatic head value of 1000mm, finding a suitable tent shouldn’t be that hard.
Hydrostatic Head Values Isn’t The Only Factor To Be Concerned About
Whilst hydrostatic head values are a good indicator of how water resistant a material is, they aren’t the only factor that comes into play when determining how waterproof your tent is.
Even a tent with a hydrostatic head of 10000mm can end up with water seeping through. This is because hydrostatic heads aren’t the sole factor.
The overall build of the tent plays a part in how well a tent can keep water out. Entry points are the crux of the problem when it comes to waterproofing. Water can seep through seams between sheets of materials and zippers.
A tent with a hydrostatic head value of 3000mm that has tightly sealed seams and zipper covers will outdo a tent with a higher hydrostatic head but a flawed design.
If you intend to stay dry in your tent, looking out for the flaws in the design of the tent is as important as looking for a high hydrostatic head. Zippers with covers are a simple way to keep water out and sealed/hidden seams are a great way of preventing water from entering.
Some tents also come with an additional layer of waterproof coating. This allows water to bead off the material and glide down the sides of the tent and into the ground instead. This provides an extra resistance to water, which will aid in keeping the inside of the tent as dry as possible.
The Groundsheet
Groundsheets typically have a higher hydrostatic head rating than the material of the tent itself. The part of the tent that will come into contact with moisture the most would be the groundsheet, hence the higher ratings.
Much like the rest of the tent, there are, however, other factors to consider when it comes to the groundsheet.
Groundsheets have to be of a certain thickness to prevent wear and tear. Even if you manage to find flat ground to set up your tent, there will inevitably be small rocks and sharp objects on the ground.
This will eventually cause wear and tear over a prolonged period of time, and holes are never a good thing when it comes to water. Worn down groundsheets are susceptible to water leaking in through the ground which would definitely lead to an unpleasant experience.
Can I Increase The Hydrostatic Value Of My Tent?
The short answer would be no. Fortunately, you can, however, increase the water-resistance of your tent. As mentioned above, there are other factors that come into play. We have gathered a few methods to help in ensuring that your tent remains as waterproof as possible and the insides remain completely dry.
Seam Sealers
A simple way to improve your tent’s water resistance would be to use what is known as seam sealers. Seam sealers help to seal the small holes between stitches at the seams. This creates a watertight seal and hence prevents water from leaking in through the seams. It can also be reapplied when wear and tear effects are noticed at the seams.
Tarps
A tarp is an excellent addition to have as well, especially when you face strong winds and heavy rain. They provide an extra layer of protection against the rain, covering any form of entry points where water can potentially seep through.
Waterproof Coatings
Waterproof coatings are also an option if your tent doesn’t already have one. We also recommend getting a UV coating on your tent as it helps with preventing degradation of the waterproof coating by UV rays. Waterproof coatings don’t last forever, so having a spare bottle of waterproof coating allows you to apply it at any point in time.
How is hydro static head measured?
Hydrostatic head is a measurement used to determine the waterproofness or water resistance of outdoor gear such as tents, jackets, and rainwear. It is commonly expressed in millimeters (mm) and indicates how much water pressure a fabric or material can withstand before it begins to allow water to penetrate.
Here’s how hydrostatic head is typically measured on different outdoor gear:
1. Tents:
- To measure the hydrostatic head of a tent, a sample of the tent fabric is placed under a cylindrical tube.
- Water is gradually filled into the tube, creating pressure on the fabric.
- The measurement is taken when water starts to penetrate the fabric, and this point is recorded in millimeters (mm).
- For example, if a tent fabric has a hydrostatic head rating of 3000mm, it means the fabric can withstand a water column of 3000mm (or 3 meters) before it starts to leak.
2. Jackets and Rainwear:
- Hydrostatic head for jackets and rainwear is typically measured in a similar way as tents.
- A sample of the fabric is subjected to increasing water pressure until it begins to allow water to penetrate.
- The measurement is recorded in millimeters (mm) and represents the fabric’s waterproofness.
- For example, a rain jacket with a hydrostatic head rating of 10,000mm can withstand a 10-meter water column before water starts to penetrate.
3. Footwear:
- Hydrostatic head for outdoor footwear, such as hiking boots, is often not explicitly mentioned as it primarily focuses on keeping water out through materials and design.
- Waterproof boots typically use waterproof membranes like Gore-Tex or eVent, which have their own hydrostatic head ratings that are not always disclosed to consumers.
4. Groundsheets:
- Groundsheets, which are used underneath tents to protect against moisture from the ground, also have hydrostatic head ratings.
- These ratings indicate how waterproof the material is and its ability to resist moisture from seeping through the ground.
- Higher hydrostatic head ratings are desirable for groundsheets to ensure a dry sleeping area inside the tent.
In summary, hydrostatic head is measured by subjecting a sample of the material to increasing water pressure until it starts to leak, and the measurement is recorded in millimeters (mm). This rating helps consumers assess the waterproofness of outdoor gear and make informed choices based on their specific needs and the conditions they expect to encounter during outdoor activities. Higher hydrostatic head ratings generally indicate better water resistance.
Traditional methods of measuring hydrostatic head (HH)
Traditional methods of measuring hydrostatic head (HH) are primarily based on manual or mechanical procedures. These methods have been used for many years to assess the water resistance of textiles and fabrics. Here are some traditional ways of measuring HH:
1. Water Column Method:
- In this method, a sample of the material being tested is clamped or sealed into a testing apparatus, such as a cylindrical tube or a test cell.
- A vertical column of water is slowly added on top of the fabric sample. The water pressure increases as the column of water gets taller.
- Technicians observe the fabric closely for any signs of water penetration or leakage.
- The height of the water column (in millimeters) at which water begins to penetrate the fabric is recorded as the HH rating.
2. Schmerber Test:
- The Schmerber test is another traditional method for determining HH.
- A fabric sample is clamped onto a test apparatus that consists of a hollow cylinder with the fabric stretched over one end.
- The open end of the cylinder is submerged in water, creating pressure on the fabric sample.
- Water is drawn up into the fabric under suction pressure.
- The HH rating is determined by measuring the height of water drawn into the fabric before it penetrates through.
3. Static Water Pressure Test:
- This method involves using a simple column of water with a known rate of flow.
- The fabric sample is placed under the column of water, and pressure is applied.
- Technicians observe the fabric for any signs of water penetration.
- The height of the water column at which water begins to penetrate the fabric is recorded as the HH rating.
4. Manual Inspection:
- In some cases, especially with thicker and more waterproof materials like leather or rubber, HH may be determined through manual inspection.
- Technicians or quality control personnel visually inspect the material after exposing it to water or subjecting it to pressure.
- They assess whether there are any signs of water penetration, such as damp spots or visible leaks.
It’s important to note that these traditional methods may vary in precision and reliability compared to modern laboratory testing equipment. More advanced methods, such as hydraulic testing machines, are now commonly used in quality control and laboratory settings to provide precise HH measurements. These advanced methods offer greater accuracy and consistency in determining the waterproofness of materials.
Nonetheless, traditional methods have historically played a significant role in assessing the water resistance of fabrics and continue to be used in some situations, especially for quality control in the textile industry.
Exploring Hydrostatic Head (HH) in Outdoor Gear
When delving into the world of outdoor gear, one frequently encountered term is “Hydrostatic Head” or HH. This crucial measurement determines the waterproofness or water resistance of various products, including tents, waterproof jackets, tarps, and drybags. In this article, we’ll explore the significance of HH across these different contexts, highlighting the essential HH values required for various products and scenarios.
HH Across Different Outdoor Gear
One of the remarkable aspects of HH is its versatility. It doesn’t confine itself to a single application but rather extends its relevance across a wide spectrum of outdoor gear. Whether you’re seeking shelter in a tent during a rainstorm, donning a waterproof jacket to stay dry in a downpour, or relying on tarps and drybags to protect your belongings, HH plays a pivotal role in determining the gear’s effectiveness.
Tent Waterproofing and HH
Consider the example of tents. To withstand light showers, a tent’s HH typically needs to be around 1000mm. However, when facing heavy rain and strong winds, the fabric faces greater pressure, requiring a higher HH—typically around 2000mm or more. This variance in HH ensures that your tent remains a reliable shelter in diverse weather conditions.
Groundsheets and Elevated HH
Groundsheets, often placed beneath tents to prevent moisture from seeping through the ground, demand an even higher HH figure. This is due to the added pressure exerted by people and gear on the groundsheet. Ideally, a groundsheet should have an HH of around 3000mm or higher to provide effective protection and maintain a dry sleeping area inside the tent.
Waterproof Jackets and Industry Standards
In the United Kingdom, manufacturers are permitted to claim that a fabric is waterproof if it has an HH of 1500mm. However, most waterproof jackets on the market comfortably exceed this threshold. It’s not uncommon to find jackets boasting HH figures ranging from 10,000mm to an impressive 30,000mm. These elevated HH ratings ensure that you stay dry and comfortable, even in prolonged heavy rainfall.
UK Hydrostatic Head (HH) Recommendations for Different Weather Conditions
When it comes to outdoor gear in the United Kingdom, the choice of gear with the appropriate Hydrostatic Head (HH) rating can significantly impact your comfort and protection in various weather conditions. HH is a measure of a fabric’s waterproofness, and different weather conditions call for different HH ratings. Here are some HH recommendations for different weather conditions in the UK:
1. Light Rain and Showers:
- For light rain and occasional showers, such as those often experienced in the UK, outdoor gear with an HH rating of around 1000mm can suffice. This includes tents, rain jackets, and tarps.
- Tents with this HH rating should keep you dry during intermittent drizzles.
In the UK the recommended HH is 1,500 so we don’t stock camping tents that are below this. How often does it rain during the summer months.
2. Moderate Rainfall:
- In moderate rainfall, where rain intensity is higher and continuous, it’s advisable to opt for gear with an HH rating of at least 1500mm.
- This includes waterproof jackets and tarps designed to withstand prolonged rain showers.
- Tents for moderate rainfall should have an HH rating of around 1500mm to 2000mm for reliable protection.
3. Heavy Rain and Strong Winds:
- When facing heavy rain accompanied by strong winds, your outdoor gear should feature a higher HH rating, typically in the range of 2000mm to 3000mm.
- Waterproof jackets designed for these conditions often have HH ratings exceeding 10,000mm.
- Tents should ideally have an HH rating of 3000mm or more to handle the added pressure of wind-driven rain.
4. Winter and Snow Conditions:
- In winter, when dealing with snow and wet conditions, it’s crucial to have highly waterproof gear.
- Waterproof jackets for winter should have HH ratings exceeding 10,000mm or even 20,000mm to keep you dry in heavy snowfall and sleet.
- Tents for winter camping should also feature elevated HH ratings of 3000mm to 5000mm to provide a reliable barrier against snow and moisture.
5. Extreme Weather and Downpours:
- In cases of extreme weather, such as severe storms and torrential downpours, look for outdoor gear with the highest HH ratings available.
- This includes waterproof jackets with HH ratings of 20,000mm or more and tents with HH ratings of 5000mm and above.
- Tarps and other gear intended for such conditions should also have exceptionally high HH ratings.
We sell a wide range of expedition tents including the Laser Compact All Season 2 tent which has a HH of 10,000. We really do a tent for all seasons.
It is worth noting, we don’t use HH for our canvas tents because it isn’t a useful measure of waterproofness for canvas fabric.
Don’t purchase a 6000HH tent to use in the height of summer, yes we got caught out and it still let rain in but this year the summer was wet, if your just doing a weekend during the summer a good 2000-3000 HH will be sufficient. If your planning on going abroad check out the recommend HH for each country.
Hydrostatic Head (HH) recommendations for tents can vary by region and climate, but generally, here are some guidelines for different countries or regions:
United Kingdom (UK):
- For the UK’s typically wet and changeable weather, tents with HH ratings of 1500mm to 3000mm are commonly recommended.
- Tents designed for occasional use may have lower HH ratings, while those intended for more frequent or prolonged use should have higher HH ratings.
United States (US):
- In the US, tent HH recommendations can vary widely depending on the region and the time of year. For general use across the country, tents with HH ratings of 1000mm to 3000mm are suitable.
- However, specific regions like the Pacific Northwest, where rain is frequent, may benefit from tents with higher HH ratings.
Canada:
- Canada’s diverse climate requires versatile tents. Tents with HH ratings ranging from 1500mm to 3000mm are often recommended for general use.
- In colder regions, where snowfall is common, tents may require higher HH ratings and specialised winter features.
Australia:
- In Australia, the choice of tent HH rating depends on the specific region. Tents with HH ratings of 1000mm to 3000mm are generally suitable for most parts of the country.
- In tropical regions with heavy rain, higher HH ratings may be necessary.
Nordic Countries (e.g., Sweden, Norway, Finland, Denmark):
- Nordic countries with their often rainy and cold climates require tents with robust waterproofing. Tents with HH ratings of 3000mm to 5000mm are commonly recommended.
Alpine Regions (e.g., Switzerland, Austria):
- Tents designed for alpine regions, where weather conditions can be harsh, should have HH ratings of 3000mm to 5000mm or higher.
- These tents are built to withstand heavy snowfall and precipitation.
Desert Regions (e.g., Middle East, Southwest United States):
- In desert regions, where rain is infrequent, tents with lower HH ratings (around 1000mm to 2000mm) may suffice.
- However, ventilation and sun protection become essential features.
It’s important to note that these are general recommendations, and the specific HH rating you need for your tent may vary based on factors like the season, expected weather conditions, and the tent’s intended use. Always consider the unique climate and terrain of your camping destination when choosing the right tent with an appropriate HH rating for your needs. Additionally, modern tent designs often incorporate multiple materials and technologies to enhance waterproofing and durability, so checking the manufacturer’s specifications is crucial.
The next time you are shopping for a tent, look out for the hydrostatic head rating that comes with it. However, keep in mind that there are other factors to look out for. That being said, hydrostatic head ratings are a good place to start with, and it helps to narrow down your selection.
This is especially true if you are planning to do some camping in the rain or snow and require a tent of a certain rating.
