What is a hydrostatic head rating for a tent?
This rating tells you how effective your tent will be at keeping you dry, but it’s not the only thing you need to look at when it comes to a tent’s waterproofing.
The hydrostatic head (HH) rating measures a tent fabric’s waterproofness in millimeters. This indicates the water pressure at which the fabric leaks.
The majority of waterproof camping tents’ ratings range from 1,000mm to 5,000mm.
Other waterproofing features (such as taped seams, zipper design, and adequate bathtub flooring) are also crucial to a tent’s waterproofing. A high HH rating without these features will still result in leaks.
Re-waterproofing is necessary to maintain the tent’s waterproof capability over time.
- Key Takeaways
- What are Hydrostatic Head (HH) Ratings?
- How Hydrostatic Head Ratings are Measured
- The Importance of HH Ratings for Tents
- How Waterproof Coatings Increase HH Ratings
- A Higher Hydrostatic Head Rating isn't Always Better
- Other Factors Affecting Waterproofness
- Maintenance and Care for Optimal HH Performance
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RELATED: Best Waterproof Tents for Heavy Rain
What are Hydrostatic Head (HH) Ratings?
A hydrostatic head rating quantifies the waterproofness of a tent’s fabric by showing how much water the material can hold before it starts to leak, and is typically measured in millimeters (mm).
Generally, a higher HH rating means greater waterproofness, where your tent material is better equipped to handle wet conditions.
Most waterproof camping tents I’ve tested have HH ratings between 1,000mm to 5,000mm, and I’ve found these to be sufficient for my usual camping trips.
I’ve also seen a few tents on the market that have HH ratings of up to 10,000mm (but I’ve never tested any of these).
Take note here that hydrostatic head ratings aren’t limited to tents though.
You may also find HH ratings in other types of waterproof gear, such as waterproof jackets and ponchos. These gear may have ratings of up to 30,000mm, way higher than what you may find in tents.
How Hydrostatic Head Ratings are Measured
Measuring hydrostatic head ratings from hydrostatic head testing is not something a typical camper (like me and you) can do.
This is usually measured in a lab, using a specialized machine, and in a standardized method by all manufacturers. This helps to produce consistent and reliable ratings across the industry.
If you’re wondering what machine is being used, this is the one. It has an actual water column within, and it replicates the downward pressure of a water column to measure the hydrostatic head.
Now, here’s how it measures the exact hydrostatic head rating.
The fabric is clamped into place, in contact with the water column in the machine. Then, the machine gradually increases the water pressure from the water column, until water starts leaking through the fabric.
The pressure at the point of leakage recorded as the hydrostatic head rating, and a manometer is used to measure how much water pressure the fabric can withstand.
For example, if a tent fabric has a 1,000-millimeter hydrostatic head rating, this means that it can withstand a water column of 1,000-millimeters without leaking. At a 1,500-millimeters water column, it will leak.
The Importance of HH Ratings for Tents
When it comes to hydrostatic head ratings for tents, here’s my advice to you.
Pro-Tip: For a tent to be considered waterproof, an hydrostatic head rating of at least 1,000mm is absolutely necessary.
I found that this rating was able to keep me dry not just against light rain, but even in a few hours of heavy rain.
If your tent has a less than 1,000mm hydrostatic head rating, this means that your tent is not waterproof, but merely water-resistant.
Here’s a quick table summarizing my findings when I was rain testing a few of my camping tents:
|The North Face
So, if you’re wondering, Coleman, Core, and Ozark Trail tents are not waterproof, and are only water-resistant. These water-resistant tents will not keep you dry in heavy rain for long.
If you’re expecting to camp in more days of heavy rain and wet weather, you could go with a tent that has a higher hydrostatic head rating of 2,000mm and above instead. If you’re interested, you can check out my review on the best waterproof tents in the market.
And while I’ve never tested tents with a 10,000mm hydrostatic head rating, I figure that they should be able to last at least a few weeks in heavy downpours and harsh conditions (provided the rest of the tent has been properly waterproofed as well).
How Waterproof Coatings Increase HH Ratings
To increase a tent’s hydrostatic head rating, manufacturers will usually always add a waterproof coating to their tent fabrics (the tent floor, tent body, and also the rainfly).
Different tent fabrics require different coatings. For example, polyurethane (PU) is used to coat polyester tents, while silicone (Sil) is used for nylon tents.
What these waterproof coatings do is to fill in the gaps between threads, increasing waterproof performance, and therefore increasing the HH rating.
A Higher Hydrostatic Head Rating isn’t Always Better
However, take note here that a higher hydrostatic head waterproof rating doesn’t always mean that the tent is more waterproof and more durable.
Three reasons why.
First, the thicker the waterproof coating on any tent fabric, the heavier the fabric gets. As such, a higher hydrostatic head waterproof rating may not always be ideal for ultralight backpackers.
Instead, they may opt for ultralight tents that have a satisfactory (but not super high) 1,200mm waterproof rating. This ensures that they will be kept dry even in hours of heavy rain and wet weather, and at the same time not packing on too much weight.
Second, a thicker waterproof coating will also result in the tent fabric becoming more rigid, and at some point, this may increase the likelihood of tearing in strong winds.
As such, tent manufacturers always need to balance coating rigidity and waterproofed-ness. (Food for thought – Why do you think most manufacturers stick with a 1,000 to 2,000mm rating, and not everyone immediately goes for a 10,000mm rating?)
And third, even if a tent has a sufficient waterproof rating, if the other features of the tent aren’t properly waterproofed, the tent will still leak.
A classic example of this is my Hyke and Byke Zion 2 (pictured above). I bought it because of its great value for money, its rainfly waterproof rating of 5,000mm and tent floor rating of 5,000mm as well.
Did it leak? Unfortunately so. Let me explain why.
Other Factors Affecting Waterproofness
There are other waterproof factors in a tent that are just as important as the waterproof rating (HH rating) of your tent. These include:
Bathtub floor height
For a manufacturer to join two different tent fabrics together, they would usually need to stitch them together. And the many stitches together form a seam between these two tent fabrics.
Each stitch in the seam is essentially a hole in the tent. I’ve found that higher-end brands tend to have smaller and more consistent holes than budget brands, which have bigger holes (leading to a higher chance of water penetration).
But whether the holes are big or small, all manufacturers need to seal up their seams using seam tape.
You can go into and check your tent to see if the seams have been taped; such seam taping should be visible, like a thin layer of plastic over the seams.
Here’s what my seam taping looks like in The North Face Wawona:
And here’s what my seam taping looks like in my REI Wonderland:
Unfortunately, my more budget-friendly brands, such as Core Equipment, Coleman, and Ozark Trail, do not always come with taped seams.
And when I was camping in these budget family tents, I found that the first place to leak is always the un-taped seams.
The second place that usually leaks next is the zippers (at least in my experience).
Pro-Tip: To deal with this, I recommend putting the zippers as high up on the tent as possible, instead of down low.
The majority of the camping tents I’ve tested so far usually come with zipper covers for additional protection. (You might also have heard others call these ‘storm flaps’ or ‘rain flaps’.)
These are usually attached over the zipper track on the outside, and effectively shields the zipper from the rain.
Some tents even have these zipper covers on the inside, to catch any pesky drops of water that happen to make it through.
Apart from tents, zippers are also potential weak points for water leakage in waterproof jackets, and these also usually have protective flaps as well.
Tub Floor Height
Another reason that leaks have gotten into my tents are because of tub floors that aren’t high enough.
As I was mentioning above, my Hyke and Byke Zion tent has a tent floor rating of 5,000mm. It also has a tub floor around the entire tent that came in at about 5 inches.
However, I found that this wasn’t high enough.
During my heavy rain test, there was a lot of back-splashing, where the rain drops hit the ground, rebounded with enough force, jumped over the tub floor, and splashed right into the tent.
After about 2 hours in the heavy rain, the entire edge of my Zion tent was filled with not just water leakage, but mud as well. It was really gross.
So, despite the high tent floor and rainfly waterproof rating of 5,000mm each, I was miserable in my wet tent. It’s like the wet weather followed me from the outside into the tent.
On the other hand, my other waterproof tents with higher tub floors of 10 inches was able to protect me from getting wet.
Overall, the hydrostatic head rating of your tent isn’t the be all and end all. There are many other factors (some of which I listed above in this section) that manufacturers and consumers need to pay attention to when it comes to a tent’s waterproofed-ness/water resistance.
Maintenance and Care for Optimal HH Performance
Now, the hydrostatic head performance of a tent isn’t a one-time setup. Consistent maintenance is a must if you want to protect the water resistance of your tent.
During any camping trip, protect your tent floors with a ground tarp. Here’s a cheap one from Amazon that you can check out.
After any long camping trip, clean the tent using a non-abrasive sponge, cold water, and non-detergent soap. All this helps to make sure that your waterproof coating isn’t scraped off or dissolved accidentally.
Please avoid machine-washing, machine-drying, and household cleaners, which can damage the tent.
I also recommend re-waterproofing your tent every 1-2 years (more often if you camp very regularly), and here’s my regular routine:
Repair tears with waterproof patching materials.
Reseal seams with a seam sealant. (Here’s the one I use for all my polyester fabrics.)
Renew the tent fly’s waterproofing by using a compatible sprays. (Here’s the one I use for all my polyester tents.)
Everything deteriorates with time, including canvas tents, so don’t skip out on this.