What is Hydrostatic Head (HH)?

When shopping for a tent or awning, you’ll often come across the term hydrostatic head in the product specifications. This technical term is essential for understanding the waterproofing capabilities of your tent. In this blog, we’ll explain what hydrostatic head means, how it’s measured, and what to look for when choosing a tent for your camping adventures.

What is Hydrostatic Head?

Hydrostatic head (HH) is a measurement of a fabric’s waterproof rating, expressed in millimetres (mm). It tells you how much water pressure a fabric can withstand before it begins to let water through. Basically, the higher the hydrostatic head rating, the more waterproof the material is.

How is Hydrostatic Head Measured?

To determine a fabric’s hydrostatic head rating, the material is tested by applying a column of water vertically to its surface. The height of the water column (measured in millimetres) is increased until the fabric starts to leak or "sweat."

For example:

• 1500mm HH: The fabric can withstand a 1.5-metre column of water.
• 3000mm HH: The fabric can withstand a 3-metre column of water.
• 4000mm HH: The fabric can withstand a 4-metre column of water.
• 5000mm HH: The fabric can withstand a 5-metre column of water.
• 6000mm HH: The fabric can withstand a 6-metre column of water.

The result indicates the fabric’s ability to resist water ingress under pressure, such as during heavy rain or when water pools on the tent.

What is Considered Waterproof?

• 1500mm HH: The minimum rating for a fabric to be classified as waterproof. While sufficient for light showers, it may not hold up under prolonged or heavy rain.
• 3000mm HH or Higher: Ideal for tents, providing better protection against sustained rain and harsher weather conditions.

For camping in the UK or other regions with unpredictable weather, it’s recommended to choose a tent with a hydrostatic head rating of at least 3000mm for peace of mind.

What About Polycotton Tents?

Polycotton tents are an exception when it comes to hydrostatic head ratings. Unlike synthetic fabrics, polycotton is not treated with a waterproof coating and therefore does not have an HH rating. Instead, polycotton relies on its natural properties:

• Breathable Protection: When exposed to moisture, the fibres swell, creating a barrier that repels water while allowing airflow.
• Enhanced Durability: Polycotton tents are less prone to condensation and provide better performance in hot and humid conditions.

While polycotton doesn’t have a specific HH rating, it is still highly effective at keeping you dry, particularly in moderate weather conditions.

Why Does Hydrostatic Head Matter?

A tent’s hydrostatic head rating is a crucial factor to consider when choosing a tent. It determines how well your shelter will withstand rain, pooling water, and high humidity. Without adequate waterproofing, water can seep through the fabric, compromising your comfort and safety.

What Else Should You Look For?

While hydrostatic head is important, it’s not the only factor to consider when evaluating a tent’s waterproofing:

• Sealed Seams: Even with a high HH rating, water can enter through poorly sealed seams. Look for taped or heat-sealed seams for added protection.
• Groundsheet Quality: A high-quality, waterproof groundsheet prevents water from seeping in from below.
• Ventilation: Proper airflow reduces condensation, keeping the interior dry even in damp conditions.

Conclusion

Understanding hydrostatic head is key to selecting the right tent for your needs. For most camping scenarios, a rating of 3000mm or higher ensures reliable waterproofing in a variety of conditions. However, if you’re considering a polycotton tent, its unique fabric properties will provide excellent protection without the need for an HH rating.

At WM Camping, we stock a wide range of tents with high hydrostatic head ratings, as well as durable polycotton options for those seeking breathable performance. Explore our collection online or visit us in-store to find the perfect tent for your next outdoor adventure!