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Keeping Your Critical Gear Dry (Part 2)

Keeping Your Critical Gear Dry (Part 2)

by , May 13, 2015

Picking up from where we left off with part 1 of our “Keeping Your Critical Gear Dry” series, kindly republished with permission from Jim Wood, we’re digging into what makes for a great gear sack…

Gear Sack Criteria

Using gear sacks to keep equipment dry can overcome most of the limitations discussed above. Besides protecting critical items on the trail, they can also provide a high measure of security while in camp. There are three key factors, however, that will determine if any particular gear sack is up to its assigned task.

1. Fabric: The gear sack fabric must be waterproof enough to provide an adequate level of protection for its contents. As noted above, sleeping bags and insulated clothing are usually the most important survival items to keep dry, but cameras, other electronics, and maps can also require the same level of protection. Utility, first aid, personal and kitchen items, on the other hand, generally need less protection, either because they won’t be harmed by getting wet, or because they’re already packaged in their own waterproof “sub-assemblies”. Food that’s stored in Ziploc bags, for example, would fall into this category.

The sack fabric must also be durable enough to stand up to real-world trail use. Stuffing a sleeping bag into a gear sack, for example, can put a fair amount of stress on the fabric – both on its sides, and on its bottom, which must be strong enough to resist punctures during this process. It’s also desirable for the inside face of the sack’s body fabric to be slippery enough to allow contents to be easily inserted and removed. Fabrics with high-friction internal coatings should therefore usually be avoided. Fabric coatings should also be able to maintain structural integrity with age. Some coatings may begin life waterproof, but can dry out and/or peel away from their face fabrics, causing cracks or other leak-inducing damage with time.

2. Seam construction: Just as important as the strength of the fabric are the techniques used to construct and seal the sack’s seams. Seams are usually either sewn, glued, or ultrasonically welded, but ultimately need to be at least as strong as the fabric itself. Sewn seams are usually either of the “simple” type, in which a line of stitching joins a single layer of fabric on each side of the seam, or of the “felled” variety, where one or more rows of stitching join multiple overlapping layers of fabric. Simple seams are typically not nearly as strong as felled seams, but unfortunately, as noted below, are often found in some ultralight “waterproof” sacks.

keeping your critical gear dry
Any seam that requires puncturing the fabric for its construction (the case with all sewn seams) needs to be sealed to prevent water leakage. Glued or ultrasonically welded seams are generally self-sealing when constructed.

3. Closure mechanism: Even if constructed from a durable, waterproof fabric using heavy-duty sealed seams, a gear bag will still leak unless it has a secure closure mechanism. The closure must be flexible enough to work equally well whether the sack is fully loaded or mostly empty. In addition, it should be convenient to use, allowing easy access to gear even when wearing gloves or mittens. And perhaps most importantly, it needs to be able to resist water penetration to the degree required by the value of its contents. Some examples of common closure mechanisms:

The ubiquitous draw-string closure that’s found on most stuff sacks is OK for organizing “ditty” items, but is pretty much useless for sealing out water when used in its simplest form.

On the other hand, if the top of the sack is twisted, then folded over and secured by tying the cord tightly around the double twist (as shown below), the closure can be made fairly water tight. Because of the twist and hook configuration, I call this technique the “candy cane” closure. It also requires that the ends of the cord be separated, and not joined with a knot, as they usually are when manufactured. In addition, for this method to work, the sack can also be only partially loaded. Further, the knot closure makes it fairly inconvenient to access gear inside the sack, can be difficult to untie if the knot becomes frozen, and if used on slippery fabrics (like silnylon), can often work its way loose with normal trail jostling. For the candy cane closure, I’ve found that wrapping a thick rubber band several times around the hook is more secure and easier to remove than a tied cord.

keeping your critical gear dry.
A variation of the draw string closure is used on sacks like the GoLite Paddler stow sack. These sacks have extended collars that can be twisted, and then folded on top of the gear contents. The drawstring can then be cinched down around the folded collar to secure it. This mechanism only works, however, if the sack is mostly full. If the sack is say half empty, this closure is of little value by itself. To prevent leakage in a partially full sack, the top collar would need to be twisted, doubled, then tied off with a separate cord as described above, before the drawstring was cinched. This design, in my opinion, offers little incremental value over conventional drawstring closures, while mostly just increasing sack weight.

Golite Paddler stow sack
Roll tops are probably the best approach for dry sack closures. When secured, multiple folds of the bag’s fabric are pressed (usually) against a stiffener that’s sewn into the top rim of the bag. If the top is rolled down as far as possible, the bag’s contents can also push against the fabric to further tighten the seal, usually creating an effective barrier to water entry.

After being rolled, the top can be latched using either a single side-release buckle located at the top rim, one or two straps (also with buckles) that run vertically along the sack, or Velcro loop-side flaps that can mate to hook-side strips sewn along the lengths of the bags. I believe that of these three latching mechanisms, the single buckle at the top (used on most paddle sacks) is probably the most versatile, since it’s generally effective whether the sack is completely full, or mostly empty. Sacks with dual side straps tend to be difficult, or sometimes even impossible, to seal at low load levels.

drysacks
Other interesting closure possibilities, which I don’t think have ever actually appeared on general-purpose trail sacks, include waterproof zipper seals such as those found on Ziploc storage bags. Even if they were used for this purpose, however, they might be problematic, since they’re often easy to force open by pressing against the sides of the sealed sacks. The water-resistant tooth-type zippers of the kind now being seen on shell jackets and pack bags are another possibility, but I don’t know if they’re considered to be truly waterproof.

Stay tuned for part 3…

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