A friend of mine asked me an interesting question I didn’t know to answer. He told me that he had got himself a waterproof tent, yet, he noticed it still got wet when he was touching it from the inside. Frankly, that isn’t something happened to me in person, at least that I was aware of. Although there is a chance it did, I just haven’t noticed it. Nevertheless, that question got me curious – why do tents leak when touched? A few hours reading across the internet brought up a few insights.
Water tends to enter your tent when you touch it because you break its surface tension – that is the primary ingredient which keeps the upper layer of water molecules bind together.
Another variable in the equation is the hydrostatic head, which is one of the tent’s fiber characteristic that keeps water out. While surface tension changes due to your touch, hydrostatic head stays the same, and might still prevent water penetration.
If you are planning on buying a synthetic, modern tent, you’ve probably come across the term ‘HH’ (Hydrostatic Head).
That is one of the main characteristics tents feature to ensure water resistance. So what is that hydrostatic head exactly?
Well, that number represents the height of a water column that fabric can resist. That may be sound confusion at first, but frankly, it doesn’t.
Just imagine you pour water upon your tent, however the water pile up in a shape of a column. The more you pour, the higher the pressure the water apply on the fabric surface.
Precisely on the point in which the pressure is maximized, you measure how tall that column is. The height in millimeters is the fabric’s hydrostatic head.
If a tent features an HH of 5,000, for example, that means it can hold a water column which is 5,000mm tall.
You should also take into account other variables, such as seams and proper zippers. A high ‘HH’ value is significant, although the tent’s entire structure is what would finally determine its water resistance.
Modern tents, which are mainly synthetic and made of nylon, feature a higher ‘HH’ value than old ones, made of canvas or cotton.
Nevertheless, it is important to remember that the hydrostatic head plays a smaller role when touching the tent from the inside, as I will explain later on.
By now we understood how tents repel water, which is mainly due to their ‘HH’ value. The higher that value is – the more water resistant your tent is.
But what is the differentiating factor? What exactly lets water to get in? That would be the capillary action.
In simple words, capillary action is the liquid ability to flow through narrow spaces without any assistance, such as pressure or gravity.
Let’s say you dip a straw inside a glass filled with water. You are probably familiar with the phenomenon of water climbing mysteriously to a certain height, without any manipulation.
On that exact concept, plants in nature gain water from the ground, through their roots. Now I want you to picture in your mind zooming in your tent fabric.
As you probably guessed, your tent features micropores in it. These pores are tiny tubes, such as capillaries.
Well, the capillary action plays the same role as with your tent. The higher the ‘HH’ value is, the lower the tent’s capillary action, and lower the chances water will flow through its pores.
The third and final ingredient in the equation is surface tension.
We now know that the ‘HH’ value describes how water resistant the tent is, and that water might still get through due to capillary action.
But what does it have to do with touching the tent, and why is that leak happening when doing so? That is mainly due to surface tension.
As you might have already known, water molecules feature cohesion forces which let them stick together.
That is why you can see a water droplet – because hundreds of millions of molecules interact with each other to form a single mass.
Each molecule attracts all its neighbor molecules. That doesn’t happen in one place – at the top layer.
That layer has no molecules from above, and as compensation, it attracts more firmly the particles underneath.
That tension between the top layer and the one from below is called surface tension. That is the tension which prevents a water droplet from penetrating the fabric.
So the hydrostatic head is the tent’s way to be water resistant, and the surface tension is the water’s way not to penetrate.
Combine the two, and you will be able to keep water outside. Nevertheless, when you touch the tent from the inside, you break the surface tension, so the only factor holding water from getting in is the hydrostatic head.
If that is not enough to keep water outside, you get yourself a leak.
Then What Can I Do About it?
The best way to avoid that leak is by reducing touches as much as possible.
First, if you are camping with a bed mattress, I suggest you change it immediately.
These mattresses are usually bulky and will increase the likelihood of you touching the tent from the inside.
Instead, I suggest you get yourself a sleeping pad, which will occupy much less space and still maintaining comfort.
You may get yourself a foam or air one; frankly, they are both great and get the job done. In addition to that, you might also consider getting a bigger tent.
If you are camping with three other people, in some cases a 4-man tent might be too small. Try getting a tent which is 1-2 persons larger instead.
You might also consider putting your gear between you and your sleeping bag.
That method will prevent your sleeping bag from getting damp. However, it won’t fix the leak issue, since touching the inner part may still occur.
Why Does it Happen in Some Fabrics While Not in Others?
After reading what was said above, you probably ask yourself – why is this happening only with specific cases?
Why does my tent get leaked while my friend doesn’t if they both share the same in surface tension?
Well, that is where the hydrostatic head comes into play. As I’ve already mentioned, two factors play the same role when it comes to water repel – the ‘HH’ value and the surface tension.
When touching the inner part, you break the surface tension; however, the hydrostatic head stays the same.
In fact, in that case, it would be the only factor that would determine whether or not water will get in.
If you know you tend to touch the inner part a lot, especially while sleeping, you should consider getting yourself a tent with a higher ‘HH’ value.
What is a High Hydrostatic Head Value?
As I’ve already said, the hydrostatic head value is not the only factor should be considered, although it is one of the most crucial.
Before approaching the ‘HH’ issue, for instance, you should also examine the tent’s seams and zippers.
When it comes to proper values, a hydrostatic head which is between 3,000 to 4,000 should be fine.
You should also keep in mind that the ground sheet would probably feature a higher number.
That is because water penetrating from underneath is a more crucial problem, and modern tents focus on that issue.
When you finally choose your campsite, please make sure to remove all rocks and broken branches on the ground.
No matter how high your tent hydrostatic head value is, nothing could help when it gets torn.
Which Products Feature Hydrostatic Head Value?
While being reasonably known in the field of tents, you may also find hydrostatic head values in other products, such as jackets.
Clothing products, which claim to be waterproof, usually feature an ‘HH’ that is much higher than tents.’
As opposed to tents, jackets are usually required to deal with much higher pressures. One of those will be the pressure your backpack straps cause while hiking.
For that reason, jackets ‘HH’ may get to values which are between 10,000 to 30,000.
Gore-Tex and eVent fabrics, for example, provide the highest hydrostatic head values and are known to be the most waterproof.
Some manufacturers, such as Polartec, claim that an ‘HH’ value greater than 20,000 is not really necessary, and may even compromise breathability.
For that, they introduced the ‘Neo Shell’ technology, which combines both water resistance and breathability.
On that matter, I would like to mention that the tent’s breathability is no less critical.
Improper ventilation might cause condensation, which may give you a hard time during the nights and mornings.
Hence, I suggest you focus on getting a more substantial tent instead of concentrating on ‘HH’ and try to minimize occupying space from inside.
Is it Possible to Improve The ‘HH’?
Frankly, that would be impossible.
It is essential to understand that the hydrostatic head is a microscopic characteristic which cannot be changed. Nevertheless, there are ways to improve the tent water resistance.
First, you should make sure your tent’s floor is sealed, and that there aren’t any leaks. In a case there are, it doesn’t mean you have to get a new one.
You can get yourself a tent tarp or a footprint, so you gain that extra layer.
In addition to that, you should also check there aren’t any leaks from your tent’s seams since these are the most vulnerable.
If they do need an extra seal, you may use tape, or maybe even a waterproof silicone spray. If none of these worked, perhaps you need a new rainfly for your tent.
While most tents usually feature a built-in rainfly, in many cases this one gets worn out, and you have to buy a new one.
Which Tents Will Prevent This From Happening?
Nothing is ever guaranteed. As you’ve already read above, even tents that feature a high ‘HH’ may leak.
It would be a safer choice to go for a tent with a high value rather than a low one. However, you should keep in mind that the higher the ‘HH,’ the more substantial the tent is.
One feature I am personally familiar and satisfied with is the Coleman WeatherTec™ system.
These tents tend to have 3,000-4,000 hydrostatic head value and therefore are impressively waterproof.
Just an anecdote for comparison – The Ministry of Defence UK has classified a hydrostatic head of 800mm as waterproof.
If you are looking for a small one, I would highly suggest you get the Coleman Sundome 4-Person Tent. This one also features inverted seams on its floor, ensuring better water resistance.
If you are looking for a large tent to camp with your family, you might also like the Coleman Montana 8-Person Tent which features the same WeatherTec™ system.
Many tents leak when touching them from the inside by accident.
This phenomenon may be extremely annoying, although there are explanations for it and a few ways to overcome the issue.
There are two main factors which keep water outside your tent – hydrostatic head and surface tension.
While the ‘HH’ is a characteristic of the tent, the surface tension is merely the reason water form a droplet mass which cannot go through the fiber pores.
Nevertheless, when touching the tent from the inside, you increase the chances of breaking this surface tension, leaving the hydrostatic head as a sole water repellent.
The best way to overcome this issue, in my opinion, is by limiting the inner occupied space. For that, you may use a sleeping pad instead of a large mattress.
A different approach would be getting a more massive tent, perhaps 1-2 persons larger. This way you decrease the chances of touching it by increasing potential space.
Well, that would be it. I hope my article brought up a few solutions and answered your questions. Let me know about your thoughts and insights by leaving a comment below!