With all the fabric advancements in the past years terms like waterproof and water resistant get thrown around a lot. But reality is such that not many products that use these terms are really literally waterproof. Waterproof as in I have dropped this backpack overboard into the sea with all my clean undies and my camera inside and I didn’t even flinch because I know water wont get inside. So to clear things up and explain what we think when we say that DryTide backpack is waterproof, I am going to divide all “waterproof” products into a few groups and explain what can you expect from each of these groups. And just to make things easier I am going to stick to bags and backpacks but this could be valid for just about anything actually – jackets, covers, sleeping bags, bivouacs, tents…
But first a short explanation about the fabrics in general. Fabrics generally aren’t waterproof. The reason for this lies in the construction – fabrics are woven together from individual fibers that even if they are woven really tightly leave some room in between them for water to get in. The width of these fibers is measured in denier. A single strand of silk is approximately one denier. So a 500 denier fiber is 500 times thicker that a single strand of silk and for instance thinner than a 1000d fiber. As said, when fibers are woven together, even when they are woven very tightly, there are still pores in between them. The thicker the fibers the bigger these holes are and easier it is for water to get through the fabric. Even if these pores are really small and water normally can not get through, with some added pressure (for instance stronger rain, underwater pressure or simply the pressure created between your body and the backpack on your back) water can still get through. So for 100% waterproof fabric it is best if there are no pores at all. One of the ways to achieve this is by laminating the fabric. Off course this kind of fabric does not “breathe”, but when it comes to backpacks this is not an issue.
So here are the 4 levels of waterproofness:
Regular materials – level 0
For a really short time just about any material will protect the inside of a bag from moisture. So running really fast from your house to your car in light rain with a regular backpack on your shoulders won’t do any damage to the things inside it. But since nothing on the material is waterproof or at least water resistant anything more than that is not recommended. Also, with bags like these term waterproof is usually not even used.
Water resistant and waterproof – level 1
Here we have bags made out of waterproof or water resistant materials. I would put these materials into two groups: materials that try to stop water and have at the same time some other functions like for instance be at the same time breathable, look or feel a certain way, have requirements about weight, shape, processing, softness etc… and then there are materials that just want to stop the water. The first level of waterproofness is achieved with materials from the first group. Depending on the price, technology and choice of these materials they will stop water for a different periods of time. But in most cases after a while they will start leaking. Either because of the friction between the material that pushes the water inside, or they get less waterproof when they get a bit older and worn out, or they just simply lose their waterproof capabilities after they are exposed to water for a longer period of time. Since these materials are not 100% waterproof the bag production itself is also not 100% concentrated on making bags waterproof, there would be no real use in that (but more on that in the next waterproof level). These bags are ok for use in lighter rain and when a dry place is somewhere close, so you know you won’t have to expose these bags to the rain for a long time.
Waterproof – level 2
Here are materials from the second group. Materials whose almost sole purpose is to be waterproof. They will never ever leak water, even when they are exposed to it for a really long time (like one year:)) because they have no pores in the fabric. But…there is always a but. The type of material used when producing a bag is not everything when it comes to making a backpack waterproof. Backpacks are not made out of single piece of material and even if they would be there is the question of openings: main compartment, pockets… you need them to put your belongings into the bag. So what is the problem? All the common production techniques involve stitching of materials and stitching makes holes. There are various ways to later seal these holes but usually, after a while, you will get leaks. So in level 2 I have put backpacks that use waterproof materials but also use stitching and possibly sealing for construction and they use regular zippers. These backpacks work good also in heavier rains and can be exposed to rain for a longer time, but eventually water can get in. Also, dropping them into the water is not a good idea.
100% Waterproof – level 3
Here we have the ultimate. Materials that are 100% waterproof and production technique that does not use stitches to put the panels together when producing a backpack. So what is used instead of stitches? The process is called Ultrasonic Welding. This is a more complicated and relatively rare construction technique. The machines used for ultrasonic welding are expensive, and they are not operated by your average sewing machine employee. The machine uses high level of ultrasonic sound waves that are directed into the fabric, these sound waves are then transformed into heat which causes two layers to bond together and form a 100% waterproof seal. No needle holes. Since this production technique is expensive it is only used for bags that really must be 100% waterproof. So in this last group we have backpacks that you can literally throw into the sea and let them float for hours and the inside will still be bone dry. You can hike all day through torrential tropic rainstorm and everything inside the backpack will be dry. You can go rafting, you can go kayaking, you can stand in the middle of the river fishing with your backpack sitting in the water and everything inside will be safe.
The Reality of 100% Waterproof Bags
Unfortunately stitching and construction is not everything. Backpacks need openings, how else would you put your belonging inside the backpack. This is where we come to the real problem. Even with ultrasonic welding and 100% waterproof construction, bags need to have openings and closing these openings and preventing the water to get in is the hardest part. Regular zippers are the worst, they are easy entry points for water to get in as they have small holes in between the zipper teeth. An improvement over regular zippers are water resistant zippers that have fabric protection over the zipper so raindrops, water splashing… can ideally not get to the zipper teeth. In reality in strong rain after a while water starts getting through. If you put these into the water, water will get in pretty fast. So best technical solution to close waterproof bags right now is the fold down closure. You fold the top of the bag tightly 3-5 times and then buckle the ends together or to the side of the bag (see the full waterproof backpack instructions here) which prevents the fold from unfolding and the backpack is sealed. The truth is that even though all waterproof bags use this system it is still not 100% waterproof, even though some people, websites etc… seem to think so. This system is simple, malfunction free, you can not mess it up, and it works well in 99% of conditions. The 1% occurs when you leave your bag floating in water for a really long time with fold down closure floating underwater or if you would even forcefully dunk the bag underwater (waterproof bags trap air inside once you close them, this air helps them float on water if you drop them into the sea) the water will slowly get in. It is not a drastic flush of water that would instantly soak your things, it’s a slow process that also depends on how tightly did you roll the top of the bag. So if your backpack falls into the water don’t worry – system like this gives you plenty of time (hours!) to save your belongings or even allows you to use your backpack in the water, but be warned that none of the dry bags are 100% waterproof in all conditions, even though many websites/stores/producers claim so. Still, this is as close as we can get to 100% waterproof without breaking the bank and making these bags insanely expensive.
There is another closing system that is rarely used because it is very expensive. It uses special zippers that are designed not to let the water in. There are two types of these zippers. The more affordable ones, but still expensive, are rainproof zippers, which we are also used in our DryTide backpack pockets. You will notice that closing this zipper feels harder and tighter than with regular zippers. These zippers will withstand rain, but if dropped into water they will slowly let water get in. The last option are 100% waterproof zippers that also work underwater. Using these would make the backpack 3 times more expensive, so we opted against them.
The danger with using zippers is that if you are not careful, and you don’t close the zipper all the way, it won’t do you much good. Even a small hole at the end of the zipper will let in more water that the fold down system in 10 hours of floating on sea. This is why we have designed the DryTide backpack using both closing systems. The big main compartment uses the fold down system that is more practical and fail proof. The two external pockets on the other hand use rainproof zippers. This makes DryTide the most advanced and innovative backpack out there.
When Do You Need 100% Waterproof Backpack?
Now the question is – do you really need a 100% waterproof backpack? It is as much a matter of needing it as it is a matter of the peace of mind. There are countless situations and sports where you really do need a waterproof backpack. But there are even more situations when owning a dry backpack will give you a peace of mind. When you are transporting expensive cameras, your laptop, your phone, your money, papers, or even just dry clothes, you want to be sure that your belongings are safe. As long as there is a chance of water getting in, you will be nervous. Even if the chance is small. I know I was. My backpack was at the back of the pickup truck and it was raining hard on the way from Padang airport to the ferry port. Even though the backpack should hold the water out it was not a dry backpack and all I could think about the whole drive was “I hope all my clothes aren’t soaking wet when we arrive.” Having a 100% waterproof backpack is knowing that is better to be safe than sorry. It is knowing that even if your backpack falls into the sea, you can just simply pick it up and go on as if nothing happened. It is an insurance that you don’t need until you need it :).