When shopping for tents, jackets, or other outdoor gear, you may have come across the term Hydrostatic Head (HH) and wondered what it means. This rating is a critical indicator of how waterproof a material is and how well it will protect you from rain, wind, and other weather conditions. But how does it work, and what do the numbers really mean? In this blog, we’ll break it down and explain the pros and cons of a high HH rating.
What Is Hydrostatic Head?
Simply put, the Hydrostatic Head rating measures the waterproofness of a material by testing how much water pressure it can withstand before it starts to leak. The measurement is in millimetres (mm), and it’s determined by placing a column of water on top of the fabric and measuring how tall the column can get before water penetrates through.
For example, a 2000mm HH rating means the material can withstand the pressure of a 2-metre tall column of water before it leaks. Which sounds a but unlikely in the real world, but read on and it’ll all make sense.
Real-World Implications of Hydrostatic Head
In practical terms, the Hydrostatic Head rating helps you choose the right equipment depending on the weather conditions you expect to face:
- 1000mm Hydrostatic Head: This level of protection is typically sufficient for light showers. In normal conditions where wind and gravity push rain onto a tent or jacket, a 1000mm rating will keep you dry.
- 2000mm Hydrostatic Head: For heavy rain and driving wind, you’ll need a higher rating to deal with the increased pressure. A 2000mm HH rating will ensure your tent or jacket holds up well during sustained rainfall and windy conditions.
- 5000mm+ Hydrostatic Head for Ground Sheets: Ground sheets, where the pressure from walking, sitting, or lying down is much greater, require a higher HH rating of 5000mm or more. This prevents water from seeping in through the base, especially when camping on wet ground.
- 10,000mm Hydrostatic Head: Some materials can have HH ratings as high as 10,000mm. This ensures maximum waterproofing and protection, even when pressure is applied by physical forces like someone leaning against the tent or branches rubbing against it in the wind.
The Downsides of a High Hydrostatic Head Rating
While a high HH rating sounds ideal, it’s important to consider the trade-offs:
- Reduced Breathability: Materials with very high HH ratings (like 10,000mm) often sacrifice breathability. This can lead to moisture build-up inside your tent or clothing, causing discomfort, particularly in humid conditions. Condensation and sweat can make the interior feel damp and stuffy.
- Increased Weight: The thicker materials required for higher HH ratings tend to be heavier. This added weight can be a drawback if you’re backpacking or need lightweight gear for long hikes.
- Reduced Flexibility: High HH materials are often more rigid, making them less flexible and harder to handle. Pitching or packing up a tent made from these materials can feel more cumbersome.
- Higher Cost: Producing fabrics with high HH ratings requires advanced manufacturing techniques and more durable materials, which can increase the overall cost. If you don’t frequently camp in extreme conditions, a lower HH rating might be sufficient, and you could save money.
Balancing Waterproofness and Practicality
While high HH ratings provide peace of mind during extreme weather, it’s essential to balance waterproofness with other factors such as breathability, weight, and cost. For most outdoor enthusiasts, a 2000mm HH rating will be sufficient for staying dry in most conditions, while ground sheets should ideally be 5000mm+ to withstand pressure from the ground.
In conclusion, understanding the Hydrostatic Head rating of your gear helps you choose the right balance of protection and practicality, ensuring you’re equipped for any adventure without unnecessary compromises.
