Understanding the hydrostatic head of the material used to produce your bell tent will help you to compare its water resistance with others. The hydrostatic head relates to the water resistance capabilities of the tent before it has been used.

Wikipedia define it nicely;

“Hydrostatic head is also used as a measure of the waterproofing of a fabric, commonly in clothing and equipment used for outdoor recreation. It is measured as a length (typically millimetres), representing the maximum height of a vertical column of water that could be placed on top of the fabric before water started seeping through the weave. Thus a fabric with a hydrostatic head rating of 5000 mm could hold back a column of water five metres high, but no more.”

Wikipedia

The Manufacturer

All bell tent retailers/manufacturers will choose to present themselves and their product in a certain positive light on-line through their websites and various other platforms. You’ll get a good feel for each supplier by comparing their on-line presence. 

However, there is a lot more to manufacturing bell tents than is presented on-line. All of which have an affect on the quality and longevity of your tent. Here follows a deeper question to ask your supplier, the reason why this question is important, what to make of their response and follow up questions to ask.

Q: What is The Hydrostatic Head of the Tent I am Purchasing?

Why This Question is So Important

The hydrostatic head (HH) of a material determines its resistance to water penetration. It indicates the amount of pressure required to force water through the material. Legally, a tent must have a HH value of 1000+ before it can be called ‘waterproof’. Canvas bell tents are usually water resistant and generally have a HH of 350-450 (polycotton tends to range between 310-380).

Compared with synthetic material counterparts, achieving HH values in excess of 1000+, and some as high as 4000! But this is at the expense of breathability, resistance to the effects of UV and detrimental effects on the tent’s longevity. For canvas, the weathering process greatly improves the canvas’ water resistance over time, and the treatments in the canvas easily can be replenished.

Bell tent manufacturers should be batch testing the material used to produce their tents, and they should be able to demonstrate the results upon request.

The Response

If unable to answer this question meaningfully, it could be that the manufacturer isn’t batch testing their canvas for hydrostatic head. HH is one of the most important tests to conduct on standard cotton canvas intended for outdoor structures. If they’re not testing the HH you’d be right to wonder if they’re testing anything at all. Other important tests include, but are not limited to:

• Tensile Strength (the force required to pull something apart. I.e – at what point does the canvas tear?)
• Flammability (if the canvas is being sold as flame resistant)
• Colour Fastness to Light (how the canvas is affected by UV)
• Breathability (measures the canvas’ resistance to air permeability)

The Follow Up

If this question remains unanswered, or the hydrostatic head is less than 350 (for a canvas tent) or 310 (for a polycotton tent), simply walk away.

A bell tent with a hydrostatic head any lower will be problematic from the start and it’s unlikely that the weathering process will be enough to help it along.