High and Dry: A Quick Guide to Understanding Waterproof Ratings at a Tent Sale

Besides considering size, weight, seasonality, and features of a tent, you should also check the tent’s waterproof rating whenever you’re at a tent sale. The fabric’s capacity to withstand everything from drizzles to downpours is essential for camping around NZ, where rain falls year-round and Mother Nature – while undeniably beautiful – can be rather unpredictable.

What are waterproof ratings?

Waterproof ratings are measured in millimetres (mm) and usually fall anywhere from 800mm to 10,000 mm. These figures indicate the amount of water pressure a fabric can withstand. That means a tent with a 2,000mm rating will endure a 2,000mm or two metre column of water bearing down on it before it starts to leak.

How are waterproof ratings determined?

To measure how waterproof a fabric is, tent manufacturers use a method called the Hydrostatic Head (HH) test. HH is the term for a material’s water resistance. They clamp sample material onto the bottom of a clear graded tube, then slowly fill the tube with water, waiting for at least three drops of water to finally seep through. The height of the water in millimetres at the point of leaking becomes the fabric’s waterproof rating. 

Protective coatings are applied to tent fabrics which close the gaps between threads, preventing water passing through the fabric and allowing water to bead and run off and maintain the quality of the material. Typically these coatings are polyurethane (PU) for polyester fabrics and silicone (Sil) for nylon fabrics. The application process, thickness and number of applied coatings are used to achieve the desired HH.

Is a tent with higher HH always better?

So it makes sense that higher HH ratings are better because they can withstand larger amounts of water pressure, right? That’s true, but also consider that an umbrella with a very low HH will still keep you perfectly dry. Tents are used for different purposes and exposed to various stresses including exposure to sunlight, rough winds and weather, handling, and abrasion from rough, damp ground. Higher HH fabrics are more rigid and heavier and may be unnecessary for the type of conditions you will be facing.

And it is important to remember that HH is only one factor in determining a tent’s overall ability to withstand water. A 10,000-mm tent can still leak if it is not stitched correctly, or the seams are not treated with heat taped seams (or applied sealant in the case of silnylon), or if the tent is poorly designed and water finds its way through places like zips or windows.

So which tent ratings are suitable for which conditions?

When all is said and done, there are general guidelines for picking the right water-resistant model at a tent sale. Usually tent floors have higher ratings than floors as they take the added stresses of campers above and constant contact with the ground below.

Consider the season you will be camping in and check local conditions where you will be heading out to see what the recommended HH ratings are best suited to that environment. In some countries two-to-three season tents typically have walls rated 1000 mm and floors of 1,500 mm but these may be inadequate in other climates.

In New Zealand, with downpours even in the height of summer 2 and 3 season tents should have fly waterproof ratings that exceed 1,500mm and floor ratings that run past 3,000mm which should withstand most winds and rain. In comparison, 3 and 4 season tents, which are suitable for camping in any month anywhere in NZ, can protect you from heavy rain and light to substantial snow and you should be looking at fly minimums of 3,000mm and 5,000-10,000mm on floors.

Having the right gear means you can focus on enjoying your adventure and not trying to stop that water dripping on your head. With equipment designed to keep you comfortable outdoors, the final question you can ask yourself is not so much which tent to buy – but instead, where are you headed next?

Email info@intentsoutdoors.co.nz for assistance.


What is Hydrostatic Head? GetOutWiththeKids.co.uk

What Does Hydrostatic Head Mean? GearWeAre.com

Tents for Camping: How to Choose, REI.com
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