Waterproofing Cotton

Not actually Erin.

Picture by KJ Photography

& is used with permission.

"Cotton kills" is an aphorism that all campers, hikers and preppers ought to know. Cotton is often called "death cloth" because wearing it in a cold, wet environment can lead to hypothermia. But do you know why?

It's because spun cotton fibers are hollow. When water meets cotton, that water becomes trapped inside the hollows of the fibers. In fact, cotton is so good at trapping water that it can hold 27 times its weight in H2O! That much water takes a long time to dry out, and when you add that to the fact that water is an amazingly efficient conductor of heat, you can see why wet cotton clothing can be a killer.

But this flaw in cotton's design can also be its salvation. If we fill those hollow fibers with something else, then water cannot clog them in first place. Ideally, that "something else" is a substance which repels water anyway, thereby making the cotton garment doubly impregnable. Most spray waterproofing substances just coat the outer fibrous layers, with the predictable result that a gap in coverage means water is still dispersed throughout the fabric. However, if we wax our cotton garment, then water will bead off it due to a combination of surface protection and an inability of it to soak in.

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There are many forms of cotton wax out there. I prefer Martexin Original Wax, which comes in a 1.5 ounce metal tin ($12 with Prime from Amazon) and which provides enough wax to treat a boonie hat. Coincidentally, I know this because that is the garment I treated my tin of Martexin; for larger items, such as coats or jeans, you will need more than one.

Application of the wax is easy, albeit messy. Martexin wax is soft and slightly sticky, like an ointment, and so I scooped some up with my finger and worked it into the fabric. I find that a circular motion works best, although you can alternate between up-down and left-right; what matters is that you coat the fibers as thoroughly as possible. Pay special attention to seams and other places where fabric overlaps to ensure that you have covered it from every angle. When you are finished the material should have a waxy sheen to its surface. In the picture below, the right side is waxed and the left side is not.

When you have finished waxing your section of garment (I suggest doing it by sections to avoid fatigue and to ensure that seams have overlapping coverage), melt the wax into the fibers using a heat source. I prefer using a heat gun as that is both fast and hot, but you can make do with a hair dryer or even a camp fire.

Be careful! All waxes are flammable to some degree, but waxes made with paraffin -- a petroleum derivative -- are especially so. Do not set fire to your waxed garment!

The heat will melt the wax, which will sink into the fabric and the surface will no longer be glossy. Your garment may look slightly darker but otherwise normal. In the picture below, you can see that the beige to the right is slightly darker than the beige to the left. 

Now turn your garment over, or inside-out, and coat the other side exactly the same way. This gives you a double-layer of protection.

If you have any wax left, pour water over your garment. The water should bead off it as if the cotton was nonporous; if you notice any wetness, you missed a spot, so dry your garment and cover it with more wax.

When you are done, you will notice that your waxed cotton garment is darker and stiffer. This is normal, although in the case of coats and jeans the stiffness will work itself out after a few days of wearing it, much like new leather.

Unfortunately, just like other forms of waterproofing this, too, will eventually fail. Hot days and direct sunshine will cause the wax to seep out of the cotton fibers, and constant flexing will crack the wax surrounding fibers at points of motion. However, touching up your waxed cotton is as simple as adding more wax and applying heat -- far easier and far less expensive than chemical waterproofing, and likely to last longer as well.

No go out there and wax your cotton!