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Materials Glossary

TOM BIHN has been making packs and bags for over three decades, and to a certain extent we've become experts about the various materials and components used in their construction. What follows is our effort to condense our rather vast knowledge into a simple glossary. Whether you're reading about our products or those from other manufacturers, we hope you'll find this information useful.



Denier 525 in a 2x2 ballistic construction
Weight 11.6 ounces per square yard / 400 grams per square meter
Abrasion Resistance (Taber Test) 10,000 cycles and still going strong
Coating 1.8 ounces per square yard / 60 grams per square meter
DWR Environmentally-friendly C6 Durable Water Repellant
Country of Origin South Korea

Why We Chose This Material

It's our dream fabric come true: ultra-durable, has a great hand (feel) and pretty light-in-weight to boot.
Image of Recycled Nylon


There are two primary types of zippers used in outdoor and travel gear these days: coil and molded tooth.

We use mostly coil zippers on our bags and backpacks. Coil zippers are made by sewing an oblique coil (imagine, if you will, a flattened-out spring or Slinky) onto the edge of lightweight webbing (tape). The coil is shaped to create the zipper's teeth. Two of these coil/tape assemblies joined together form a continuous length of zipper chain; we get ours from YKK® in 100 meter rolls.

Molded tooth zippers are more of what people imagine when they think of a zipper: individual teeth are molded in series onto the edge of the tape. Each of these styles have advantages and disadvantages. Significantly, coil zippers tend to operate more smoothly, especially when going around curves and corners (our bags tend to have lots of curves!); tooth zippers tend to bind up and jam when negotiating corners.

One instance in which tooth zippers excel is with separating zippers (like on the front of your jacket): the separating mechanism itself is the same plastic as the teeth and is molded into the zipper tape, which allows for very tightly engineered tolerances, and therefore excellent alignment of the zipper teeth when you're starting the zipper. With a separating coil zipper, the mechanism is metal pressed onto the tape. The teeth don't always align perfectly when you're starting the zipper; additionally, the pressed-on mechanism tends to fail relatively early in applications that get a lot of use (like the front of your favorite jacket). Our designs don't use many separating zippers—if we use one and it's going to get lots of separating and un-separating (like on the Hero’s Journey), we'll use a tooth zipper instead of a coil zipper.

Zippers come in different gauges or tooth sizes, nominally measured as the width in millimeters of both halves of the zipper teeth when joined together: we use #3, #5, #8 and #10. We use the larger sizes (#8’s and #10’s) on the outside of most of our bags as they will last longest in these applications; #5’s are great for interior pockets and pouches, and #3’s are good when you’re really counting the ounces.

We use YKK®’s Aquaguard® coil zipper in many applications: it has a urethane coating on the flat side that makes it highly water repellant (though not waterproof). We originally did what other manufacturers did and sewed our Aquaguard® zipper in "upside down," that is, with the coating exposed. This has two advantages: first, the customer knows for sure that the zipper is coated because they can see the coating; and second, water is repelled before it can soak into the zipper tape. However, after doing this for several years, we saw that the urethane coating didn't last quite as long as we'd like when exposed to the wear and tear of the outside of a bag or backpack. In 2015 we started sewing Aquaguard® zippers in "right side up," putting the urethane coating on the inside of the bag (just as we do with our urethane-coated fabrics). You can still see the glossy coating—you just need to look inside the bag. We’ve found the effect on the short term water-repellency of our bags to be nominal, if any; in the long term, the zipper’s coating is safely protected inside your bag and will last longer.

One of The trade-offs of the Aquaguard® zipper is that it requires a little bit of an extra tug to open and close the zipper due to the fact that the same urethane coating that makes the zipper water-repellant adds a tiny bit of thickness to the zipper tape, which creates a small amount of additional resistance. (It’s worth noting that the Aquaguard® zipper is far easier to open than the truly waterproof zippers found on bags designed to be 100% submersible in water.) Some folks don’t notice that little bit of extra resistance when zipping open their zipper while others do. We’ve experimented with various zipper lubricants to see if there if we could find one that we felt confident in recommending to those of you who would prefer a zipper that opens like butter.
To date, we haven’t found one that meets our criteria, which is:

  • Must be environmentally friendly.
  • Must make a significant difference in the experience of opening the zipper.
  • Doesn’t add so much gunk that dirt, dust, and pet hair get trapped in the zipper, potentially making the zipper feel more sticky in the long run.

We (and most of you, as far as we hear) feel the trade-off is worth it, and that’s why we choose to use Aquaguard® zippers on many of our bags. As always, your thoughts and feedback are wanted:

As mentioned above, when Aquaguard® zippers were first introduced, everyone sewed them in upside down. Now, many manufacturers sew uncoated zipper chain into their bags (and jackets, etc.) upside down, utilizing the reverse zipper sliders originally developed for Aquaguard® zippers. We're not sure why this is done: maybe some folks think the flat side of the zipper looks cooler? (One of the downsides to doing this is that it can confuse customers into thinking that the zipper is "waterproof" when it actually isn't.) Furthermore, coil zippers are engineered to bend around corners and curves when the teeth are on the outside of any curve. The coil zipper chain bends far less well when reversed, and will actually tend to wear out prematurely. We do this trick of sewing uncoated zipper chain upside down only on the back pockets of the Side Effect and Side Kick, with the thought that since these zippers might end up against the user’s back or hip, the flat side of the zipper might be a bit more comfortable.

The gizmo on the zipper that opens and closes it is called the slider; the thing on the slider that you grab onto is called the pull. We designed a special “medium” length zipper pull because we didn’t like YKK®’s long pull nor their short pull; like Mama Bear, we wanted the one in the middle that was just right. Our metal zipper sliders are made of zinc alloy and are plated to look nice and resist further oxidation. On many lighter-duty applications we use a molded plastic slider: it won’t scratch sensitive electronics and also won’t trigger a metal detector (important for items like our Travel Money Belt). We’ve been impressed with the durability of these plastic sliders and have seen virtually no failures. Our bigger bags now come with a generous supply of cord zipper pulls which you can add to your bag yourself if desired. There's a video here that show you how to add them.

We use YKK® zippers exclusively—they’ve been at it for a long time and they know their stuff. We could save a buck or two going with a generic zipper.... but after all we do to make the best bags, that would be silly!