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Dry Bags 101

Posted by Darren Bush on 12/3/2013 to Camping Skills & Tips

Not long after humans first became conscious of themselves and their environment, I can only assume that they discovered that water, while good for many things and essential to life, really messed things up if it ended up where it didn’t belong.

Most often the biggest problem with moisture is against your skin, where you lose body heat something like 40 times faster than if your skin is dry. That’s good if you’re overheated and trying to stay cool by perspiring. That’s bad if it’s 40 degrees and drizzling. Anyway, that’s the biggest problem with moisture.

The second (and a close one) problem with moisture is when it gets on your stuff. Food can spoil if left damp, and that fish you worked so hard to dry to keep it over the winter turns green and fuzzy if you let it get damp. Same with your clothes – leave a t-shirt rolled up in a damp beach towel and drop it in a plastic bag and leave it in your truck for a season. You will find a natural tie-dye that is not flattering to the eye or the nose.

Dry bags are just the thing, especially for us paddlers who depend on them to keep our down sleeping bag dry, our dehydrated food in its preserved state, and our tents and tarps mildew-free. Water and gear don’t mix for the most part, and it’s even more evident as people become more enamored of taking their personal electronic devices into the wild.

Dry Bag History 101

Dry bags are nothing new. Wax-impregnated canvas with tight seams and a good piece of cord around the top were keeping things dry a hundred years ago. The problem is that they were not that reliable. They become stiff in the cold, melted in the heat, and there are critters that think wax is a nice appetizer on the way to the canvas. Sure, you can treat the canvas with rubber or insecticides or both, but then we’re getting heavy and toxic. So people at that point mostly went to dry boxes and barrels, which were hard (good so you don’t crush things) and a little more convenient. River trippers still like the hard boxes where space is not an issue.

As materials technology advanced, coated fabrics became available for commercial use (they had been in the military for years, apparently). Usually a nylon cloth with a waterproof coating, these fabrics revolutionized the outdoor industry (and a lot of other industries as well). Backpacks made of a tough Cordura or a rip-stop nylon were coated with a thin rubberized coating (usually urethane), so water could not get through the cloth. Hopefully, with some Scotchgard or similar product, water beaded up and ran right off. When it didn’t, it would hit the membrane and stop there. Wet pack, but dry stuff. Unless you had a leak at a seam, which leaked like sieves until you caulked them up with some seam sealer.

The coatings were not that durable. They were temperature sensitive, and sometimes peeled away completely from the fabric. More often, they simply abraded off, like my old Jansport D-2 backpack where the end of the handle of the cook kit rubbed on an area and stripped it of coating. At any rate, they were not really useful for truly waterproof gear on a reliable, repeatable basis.

PVC – The “Miracle Material”

Then PVC (polyvinyl chloride) came on the scene. Used at first for pipe (that white stuff in your house is PVC), it quickly moved into other areas of usefulness, and when calendared on a substrate (spread thin on cloth, for example), or extruded with fibers of some sort imbedded, it is completely waterproof, relatively flexible, and relatively inexpensive.

The first dry bags were made of a PVC cloth were quite a step up from the previous bags of coated nylon. They could abrade and still retain waterproof status, as the material itself is waterproof, not simply the coating. The biggest advance, however, was radiofrequency (RF) welding. PVC lends itself to RF welding and it’s an amazing technology. Basically, if you take two pieces of PVC cloth and pass a very high intensity radio wave through it, it melts the PVC and the two pieces become literally one, and at the molecular level.

Are their downsides of PVC? One is obvious to anyone who reads the newspaper. PVC is fairly toxic to produce, and contributes to the depletion of the ozone layer. Burning PVC releases toxic fumes into the atmosphere, both globally and locally (around your campfire). Doesn’t mean it’s bad material, as we need to make decisions about how we use resources. One PVC bag that you take care of and use for twenty years is better than throwing away five coated nylon bags that lose their coating and hence their waterproof nature.

The other downside is temperature sensitivity. PVC cloth becomes very stiff in cold temperatures, and becomes difficult if not impossible to roll closed so that it retains a waterproof seal. This is where coated fabrics shine.

The Other Revolution

As PVC bags proliferated, the science of coating fabrics became more and more advanced. A decade ago some scientist at Dow or 3M or Monsanto figured out a urethane coating that bonded better with cloth. It was a godsend. At the same time the methods for attaching these coatings to the cloth became more and more sophisticated. Now coated cloth was available to rival the waterproof characteristics of PVC. They are lighter, easier to roll closed, slide nicely over surfaces where PVC bags stick (like the damp inside of a kayak).

The only problem is that it is still a bit more labor intensive to manufacture coated cloth dry bags than PVC bags, and the materials cost a lot more than PVC (urethane ain’t cheap). Moreover, they’re slightly more costly in labor because of additional finish work. Urethane-coated nylon cloth is still RF welded, so it’s molecular in its bond strength too – you’ll peel the coating off the cloth before you separate the layers from each other.

Value vs. Price

I gotta preach a little here.

Lots of folks use “value” when the mean “cheap.” “It’s a good value” is Walmartese for “Look how cheap we are! Cheap cheap cheap!!!” I am not using the word that way. Value means to me that the cost of the item is less than you would expect given a level of performance desired. Things with good value are things that cost less and deliver more.

The bottom line is that the only true disadvantage of urethane-coated cloth drybags is price. This doesn’t mean that if you have money to burn you should buy nylon bags. You should buy the bags that suit your needs. If you have the extra cash and you’re going to use your bags a lot, nylon is probably the best value. If you’re an occasional paddler, you are probably just fine sticking with PVC.

I’m a good example of that. My kayaking gear is nylon, my canoe gear is PVC. Why? I use the kayak gear more often than the canoe gear, roughly four times more. The PVC stuff I have I’ve had for six or seven years now, and I’ve taken good care of it. It’s in fine shape. I plan to keep it for another six or seven. There are a few little holes in it from my blunders on rock-strewn portages, but duct tape and Aquaseal have taken care of them.

Size Matters

It actually makes a difference what size a bag is in terms of keeping its contents dry. Roll-top closures seal better when there’s a little pressure inside, helping the bag keep its shape. It’s best to have a bag two-thirds to three-quarters full, allowing space to clear out the excess air and achieve a good closure.

Bags are sized in liters (approximately 5% more than a quart). A 5 liter bag is a small one, holding in reality less than a gallon because you can’t fill them up all the way. In terms of what you can store in a particular bag, below is a guideline that is very rough and highly subjective, but it’s better than no guide at all.

5-liter bag: Small personal items such as medicines, a first aid kit, a toiletries kit (a roll of paper squashed with the core removed and some hand sanitizer, for example), a small lunch, etc.

10-liter bag: A more convenient way to store personal items. Holds twice as much as the 5 (of course). Good size for a decent-sized lunch and a first aid kit.

20-liter bag: A smaller sleeping bag, a few days worth of clothes, a kitchen kit with a backpacking stove inside it, a long weekend’s worth of freeze-dried food for two people, etc.

30-liter bag: Sleeping bag (synthetic), a week’s worth of clothes if you squeeze it a bit, a week’s worth of freeze-dried or dehydrated food, all the kid’s sweaters and extra clothes for when the canoe turns over.

A few things I’ve learned over the years…

1) A SeeBag (the clear ones) in the 5 or 10 liter version is a great diversion for children. Kids can set up mini aquaria along the beach where a bag of water, some sand, and some sand crabs or minnows or crayfish can provide hours of educational enjoyment. Just be sure to put the little critters back where they go before they cook in the hot sun.

2) Animals can’t find what they can’t smell. If you keep the outside of a dry bag food smell-free, you can stash them away from camp and generally have good luck. I’ve never hung food, preferring to hide it. Just my opinion.

3) All bags should be washed and hung in a place to dry after trips. Storing bags loaded is a bad idea, and letting bags air out is a good thing. Turning them inside out is sometimes a good thing for sand management. Sand wears out bags prematurely by grinding away coatings.

4) If you’re packing a sea kayak or backpack, buy more smaller bags rather than fewer big ones. It’s much easier to put smaller bags through hatches, and for organizational reasons it’s best to have more compartments.

5) Color coding bags is an excellent way to keep life simple. Green for clothes, blue for food, yellow for first aid, etc. (Choose your own colors for what makes sense to you).

6) One word: Sharpies. Use them and your bags will stay yours. Big letters are easier to see than small ones. Use lots of colors and go nuts with them. I developed an emblem of my initials and used that so I could identify my stuff in a group quickly and easily.

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