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.
Aether is an ultra-light, 100% nylon fabric from Japan. It has a unique and complex construction, combining 30 denier monofilament (warp and weft) with both 100 denier and 200 denier yarns in a micro-ripstop weave to further increase its tear strength. Like most of our fabrics, Aether is coated on the backside with urethane for weather resistance, as well as having a surface treatment of durable water repellant.
This is a very light fabric, useful for those trying to save weight wherever possible. Though its hand is a bit crisp or papery when new, we greatly prefer Aether's esthetic over commonly available silicone-coated nylons. It's light, but surprisingly tough.
Original 1050d HT Ballistic Nylon
Our U.S.- made 1050 denier high-tenacity (type 6,6) nylon ballistic fabric was originally developed for use in flak jackets and bullet proof vests, hence the name "ballistic."
In the 1980s ballistic nylon was replaced by Kevlar fabric for use in personal armor; fabric mills began offering it to the outdoor and luggage industries. The luggage industry adopted it for use in soft bags as it did not abrade clothing, particularly women's nylon stockings.
Like 420 HT Parapack, ballistic nylon is a filament fabric (not texturized) and therefore has the following advantages over Cordura®: it allows a bag to slide easily in and out of tight overhead bins, etc.; in use, it tends not to destroy clothing that it rubs against; it tends not to collect lint from sweaters, etc., and "pill"; it does not collect snow; and, very significantly, it does not collect pet hair.
Because it's a high-tenacity nylon, it does not take dye as readily as the cheaper nylons: you will sometimes notice an almost heathery sort of appearance to this fabric.
When compared with 1000 denier Cordura® fabric, 1050 ballistic fabric has virtually the same abrasion resistance. 1050 ballistic has a higher tear strength than 1000d Cordura® (though neither fabric can be easily torn in normal use).
1050 denier Ballistic is woven with two plies of 1050 woven as one, which gives it its sheen and substantial feel. 1680 denier "Ballistic" cloth is not typically a high-tenacity fiber, and does not have nearly the same abrasion resistance as our 1050 denier Ballistic fabric.
Our 1050 denier Ballistic has a urethane coating on the backside (the inside of our packs) and a Durable Water Repellant treatment (which you can't see) applied to the face side (the exterior of our bags). The exterior DWR makes water bead up on the surface and run off, and the urethane coating acts as an impermeable waterproof barrier.
525 Denier HT Ballistic Nylon
Our 525 denier HT Ballistic nylon is a lighter weight version of our 1050 HT Ballistic nylon with a twist. Literally, it’s the same construction of two yarns woven side-by-side in a basket pattern (which is what has come to define a “ballistic” weave), but with the added feature of the individual yarns being twisted as they are laid down. This twisting mitigates the potential effects of abrasion by sending any broken filaments on the surface of the fabric back into the weave, instead of leaving a broken filament lying loose on the surface.
Even though the yarns are one half the size (525 denier as opposed to 1050 denier), they are packed more closely together. As a result, the 525 fabric weighs about 70% of the weight of the 1050 fabric, not 50% as one might assume. Smaller yarns = tighter weave.
Our 525 denier HT Ballistic nylon has a very similar look and surface feel as our 1050 HT Ballistic nylon; its abrasion resistance is right in there with the 1050d, testing at over 10,000 cycles on the Taber machine. It shares the luxuriant sheen of 1050 Ballistic—if anything, it looks even richer. It has just about the same weight (10.5 ounces per square yard / 360 grams per square meter) and body as 1000 denier Cordura@, sans the fuzzy texture. This makes it an ideal all-around fabric for many applications, as it won’t collect pet hair, sweater lint, or snow.
We’ve treated this fabric with an extra-heavy urethane coating (1.80 ounces per square yard / 60 grams per square meter) on the inside; the exterior features an environmentally-friendly C6 Durable Water Repellant (DWR).
This fabric is woven and finished in South Korea with Invista Cordura® yarns from Canada.
If it sounds like we’re in love with this fabric, it’s because we are.
210 Denier HT Ballistic Nylon
Our 210 denier HT Ballistic nylon certainly pushes the limits of what we tend to think of as “ballistic” nylon. Though it is 1/3 the weight of original 1050 Ballistic (5.8 oz per sq yard / 195 grams per square meter), it’s made with the same construction of two yarns woven side-by-side in a basket pattern. It’s basically the little sibling of our 525 denier HT Ballistic nylon, and features similarly twisted yarns (see the description of 525 denier HT Ballistic nylon for the skinny on why twisting the yarn is important).
Our 210 denier HT Ballistic nylon has a similar matte look and smooth feel as our 1050 HT Ballistic nylons. It is similar in heft to 420 HT Parapack, and weighs about 25% less yet tests higher for abrasion resistance (over 5,000 cycles on our Taber testing machine). It's an excellent fabric choice for linings, dividers and accessories.
Because our 210 denier HT Ballistic nylon is intended as a lining/interior fabric, we’ve given it a relatively light urethane coating on the inside (0.85 ounces per square yard / 30 grams per square meter); the exterior features an environmentally-friendly C6 Durable Water Repellant (DWR).
This fabric is woven and finished in South Korea with Invista Cordura® yarns from Canada.
In the latter part of the 20th century, injection-molded plastic buckles and fasteners replaced most of the components of bags and backpacks that had been previously made of metal. Plastic parts are lighter weight and won't corrode, and are more pleasant to the touch, especially when it's cold.
Many of the plastic parts used on modern bags are one-for-one copies of the old metal parts, one exception being "side release" buckles (often still called Fastex buckles, after the original company that introduced the design). The precision of the injection molding process, and the careful formulation of the plastics themselves, allowed engineers to build these now ubiquitous buckles so that they're flexible enough snap together, and rigid enough to stay snapped. The basic concept of the over-centering, interlocking prongs is now used by buckle makers around the world to offer a myriad of side-release and similar fasteners.
Most of these plastic parts are molded of either nylon or acetal: both materials have advantages and disadvantages. Nylon is a bit softer than acetal—this especially of note when used in the above-mentioned side-release buckles: nylon parts don't snap together with the same crispness that acetal parts do, making the nylon quieter and less likely to pinch your fingers in use. However, unlike acetal, nylon can absorb a small amount of atmospheric moisture and when the temperature drops below 32F/0C, this tiny amount of moisture can freeze and cause the buckle to become brittle and break.
Metal parts can still offer the greatest strength and durability in certain applications; for example, die-cast zinc is used in swivel snap-hooks for shoulder straps, and brass in grommets and snaps. However, whether it's plated or painted, the surface coating on metal parts can scratch and wear over time, revealing the base metal beneath.
We'll use plastic and metal hardware on our bags, whichever provides the best utility and durability for a specific application. For plastic components, both nylon and acetal are utilized: for the side-release buckle closure on a bag's flap, for example, we use an acetal female half and a nylon male half—this combination leverages the best performance from both materials. Our metal snap-hooks are electrostatically plated black twice, just to be sure.
Most of our fabrics utilize two treatments to make them as weatherproof as possible:
The exterior surface of the fabric gets a treatment of DWR (“Durable Water Repellant”), which is more or less what ScotchGard® is. This chemical is applied to the face of the fabric, encouraging water to bead up and run off rather than soaking into the yarns and through the weave of the cloth. DWRs are the first line of defense against moisture getting into your bag.
Unfortunately, the chemicals used for DWRs do not bond permanently to the fabric's surface. This means that from time to time, you may need to renew the treatment to maintain your bag or pack's weatherproofness (see below). DWRs' non-permanence is also bad for the planet because after departing from the fabric, these chemicals tend to persist in the environment and are not good for people or other life forms. For decades the chemical of choice was an eight carbon chain PFOA (perfluorooctanoic acid). Like the rest of the industry, we’ve moved to six chain PFOS (perfluorooctane sulfonate), which breaks down much faster into simpler and (theoretically) more benign chemicals. As we move forward, we will remain on the cutting edge of environmentally-friendly DWRs.
As noted above, you may need to renew the surface water repellency of your pack or bag as it ages. We recommend NikWax Tent and Gear Solarproof: we’ve found it’s easy to apply and works well. Nikwax assures us that their product is environmentally safe.
On the backside of most of our fabrics is a coating of urethane, which is more or less waterproof. That said, water that has saturated the weave of the fabric itself will eventually soak through even this coating, which highlights the need for DWR on the front side. While the urethane coating is more durable than the external DWR, over time it can decay from abrasion, oxidation, mildew, and extensive flexing of the base fabric.
In fact, urethane coatings are one of the shortest-lived of all components in our bags—and those of other manufacturers. Because the amount and type of urethane coating can greatly impact the base fabric's tear resistance, a thoughtful choice must be made to balance the competing (or even conflicting) demands on the fabric and the finished bag. A thicker coating can give longer-lasting waterproofing, but can also make the fabric more brittle and subject to tearing; additionally, a thicker coating can have enough inherent tensile strength to make it peel away from the fabric. In our opinion, the coatings we've chosen offer a balance of durability in terms of both waterproofness and fabric strength.
Urethane coating can sometimes become slightly opaque or white over time. We've found this can be a result of the climate in which a bag is used and/or stored (particularly high humidity climates), or to chemical reactions to certain soaps or cosmetics that are either carried in the bag or used to clean it. Generally, this clouding of the urethane coating is purely cosmetic.
As a bag ages, some peeling or degradation of the urethane coating can be expected, especially where the fabric is subjected to excessive flexing (around zipper openings, for example), or excessive internal abrasion (like from the corner of a laptop or tablet). Though this can have a minor effect on a bag's waterproofness, we consider it within the realm of "normal wear and tear.”
There are a few things you can do to prolong the life of your bag's urethane coating. Most important is to make sure to dry out the inside of your bag after it has become wet, whether from something having been spilled inside or from weather soaking through. This is important if you’re storing the bag for any extended period, particularly in high-humidity climates. The urethane can actually get mildewed: you’ll know this is happening because it looks bad (and smells bad, too). To protect the coating from abrasion, you can avoid carrying items that have sharp corners that will poke/wear on the inside of the bag.
The urethane coating on our Halcyon fabrics is not quite as thick as on other fabrics. This is because the UHMWPE yarns cannot survive the heat curing that all-nylon fabrics get when they are coated. Our mill in Japan has developed a proprietary “dry coating” technique that does allow them to apply a coating, but it’s not as thick as standard heat-set urethane coatings. It’s a compromise.
Note that while our fabrics are very weatherproof, they are generally not entirely waterproof. Additionally, our bags are sewn rather than welded or glued together, and are therefore not submersible.
Modern dyes allow synthetic fabrics to attain (and hold) almost any color we humans can imagine. With such a myriad of choices from which to make outdoor and travel equipment, perhaps restraint is all that we as designers lack. Indeed, some colors and color combinations seem in hindsight to have been such bad ideas that we ought now blush.
When choosing the exterior color for a bag or backpack, it's worth considering whether you need your bag to stand out or blend in. Depending on where and how you travel, this could go either way.
For years, the wisdom in outdoor equipment was to go for bright colors so that you can be found in emergency situations. But when the backcountry started getting more visitors, and the landscape became decorated with red and orange hikers and their gear, colors that blended in became de rigueur. Greens and browns blend well in many outdoor situations, while black and grays might be effective camouflage in urban settings; blues can stand out but still not be visually irritating.
It's good to keep in mind that if other people can't see your bag, maybe you can't either, and you may be more likely to lose it or leave it behind, or be unable to distinguish it from a pile of everyone else's bags. Perhaps choosing a less common color that is yet somewhat subdued can be a compromise. You might be looking at your bag for some time, so if the color makes you smile, all the better.
The interior of a bag is likely to be seen only by you, the user, so you needn't feel so constrained in your color choices. Note that lining a bag with black fabric is a great way to turn it into a prop for a magic show: put clothing and gear into the bag and presto!—they disappear. Light or bright colors allow you to better see the contents of your bag, and a bright interior color can be a fun way to personalize your bag without being too colorful (not that there's anything wrong with that!)
A few backpack and bag fabrics are available to manufacturers "off the shelf" in stock colors. However, if a specific color is desired, you must purchase a "dye lot" of that color, ranging from several hundred to a few thousand yards, depending on the fabric and mill.
At TOM BIHN, we are known for our colors and color combinations (what the industry calls "colorways"). Most of our fabrics are dyed to our specifications and are uniquely ours: our fabric suppliers are regularly "dipping" new swatches based on color samples we submit to them to match. Over the years, we've sent them packets of spices, flower petals, paint chips, and snippets of textiles from other industries. The majority of colors don't make it past this initial stage, but we do like to offer new choices every year. We take more chances with interior colors, though you will see new exterior fabric colors as well. We do not subscribe to any of the fashion or trend services that "predict" (and then end up dictating) next year's colors and styles: as with most other aspects of the TOM BIHN business, we do our own thing, listening to our customers a bit, and mostly following our own sense of aesthetics.
500 denier Cordura®
500 denier Cordura® is slightly lighter weight version of 1000 denier Cordura®. It has good abrasion resistance, more-than-adequate tear strength, and excellent dyeability; 500 denier Cordura® can thus be a very good, all-around bag fabric.
Note that while the denier (weight) of the fibers in 500 denier Cordura® is one-half (50%) of the 1000 denier fabric, it's a more densely woven fabric: because the fibers are smaller in diameter, they can be packed more closely together. So while the fibers are half the weight, there are more of them, making 500 denier Cordura® fabric roughly 2/3 the weight of 1000 denier Cordura® fabric.
For several decades, 500 denier Cordura® was our first choice as an interior fabric, as well as for accessories and even for some exterior applications. However, it shares 1000 denier Cordura®'s affinity for lint and pet hair, so we've been replacing it with filament fabrics like Halcyon 200d and 420d HT Parapack.
1000 denier Cordura®
1000 denier Cordura® fabric was originally developed as a fiber to incorporate into automobile tires as belting. In the 1970s, Dupont introduced it to the outdoor industry as a fabric for backpacks and other gear. Prior to the introduction of 1000 denier Cordura®, most outdoor backpacks were made of 420 denier HT nylon Classic Parapack. Because it isn't high tenacity like 420 denier HT nylon Classic Parapack or our 1050d US HT ballistic nylon, Cordura® is relatively easy to dye, and is available off-the-shelf in a wide variety of colors.
Denier is a measurement of the size (weight actually) of the yarn from which a particular fabric is woven. It is the weight in grams of 900 meters (that's a little over half a mile!) of the specific yarn. The yarns, in turn, are spun of smaller fibers which can also be measured in denier. We are referring to the size of the yarn, and not the size of the individual fibers.
1000 denier Cordura® has a urethane coating on the backside (used for the inside of our packs) and a Durable Water Repellant treatment applied to the face side (used for the exterior of our bags). The exterior DWR treatment causes water to bead up on the surface and run off, while the urethane coating acts as an impermeable waterproof barrier. DWR is a surface treatment and can wear off over time. It's easy to see if the DWR is still present and working simply by dribbling a few water droplets onto the surface of the fabric: if the water soaks into the fabric without beading up and running off, the DWR has worn off. It can be reapplied by anyone using Nikwax Tent & Gear Spray or a similar product.
1000 denier Cordura® is a texturized fiber: air is blown through the fibers as they are extruded which causes some of the fibers to become discontinuous. This basically makes the surface of the woven fabric "fuzzy", creating an appearance similar to that of cotton canvas. The discontinuous fibers also absorb some of the energy of abrasion by moving (picture tall grass in the wind). The fibers also help to hide damage to the surface of the fabric caused by abrasion: the fibers broken by abrasion are masked by the already "broken" discontinuous surface fibers. Discontinuous fibers collect much more lint, pet hair, fuzz and snow than filament fibers (420d HT nylon Classic Parapack and our 1050d US HT ballistic nylon are both filament fiber fabrics). Because of its texture, 1000 denier Cordura® frays less at its cut edge. With modern coatings on the backsides of the fabrics, this is typically not a problem; buy a vintage 1000 denier Cordura® pack off eBay and you might see how this used to be an issue. Because we finish 100% of any exposed internal seams on all of our bags, this has never been an issue or consideration for us.
In 2004, Dupont sold its fiber division to Invista. Since then, Cordura® has evolved to be a brand name and umbrella for a wide variety of fabrics, some with discontinuous fibers and some not. When we refer to Cordura®, we're just referring to the original texturized fabrics.
A large variety of cellular foams are used in making bags and backpacks: some provide cushioning to the user (shoulder straps and handles), some provide protection for items carried (laptops, etc.), and some give a bag body or rigidity.
The density of foam is generally described in pounds per cubic foot (pcf). Density range is anywhere from 1.5 pcf to 20 pcf; lower densities tend to be somewhat soft, and higher densities firmer or more rigid. Foam's properties are further determined by its base material (and various additives), and whether it is open- or closed-cell.
Polyethylene is the base material most commonly used for the foams used by the outdoor and travel goods industries. Linear-linked polyethylene foam is generally used for packaging materials and is not very durable, though sometimes very inexpensive bags will use it. Cross-linking the polyethylene molecules enhances tear and tensile strength and creates a finer cell structure, making cross-linked foams more resilient and durable. Adding a small percentage (8-15%) of EVA (ethylene-vinyl acetate) to cross-linked polyethylene foam gives it a more supple, rubber-like feel; without the EVA, polyethylene foam can be somewhat stiff and boardy, which can be just what is required in certain applications.
With closed-cell foam, the "cells" are discrete bubbles of gas, completely sealed inside the base material: water and air cannot pass through or circulate within the foam. In open-cell foam, the cells are interconnecting bubbles which can allow water or air in: the sponge in your sink is a good example of an open-celled foam. Closed cell foams won't compress as much as open-cell foams because the air cannot escape the base material; even the softest closed-cell foams are firmer than open cell foams. The use of open-cell foams in areas that might get exposed to water, either from perspiration or the weather, is problematic: even when encased with "water-proof" fabric, open-cell foams can be hydrophilic and actually draw moisture in from the environment.
Poron® is an exception to many of the rules: it is a poured urethane foam that is very dense and yet very soft; though it is open-cell, it absorbs very little moisture. Poron® is generally too heavy for extensive use on a bag, but wrapped in fabric it makes a great handle. Cushy and inviting to the touch, it has phenomenal resilience and won't break down or go flat over time.
Halcyon 200 denier
Halcyon 200d is a high-tech, high-performance alternative to the ubiquitous "oxford" cloths commonly used in backpacks and travel bags for interlinings, internal dividers and accessories. Halcyon 200d is a ripstop fabric woven of 210 denier nylon (base fabric) with a square grid of 210 denier UHMWPE (ultra-high-molecular-weight polyethylene) yarns every .25" / 6mm; an additional diamond ripstop pattern adds to its sophisticated aesthetic.
The grid of UHMWPE adds no weight but makes Halcyon 200d virtually impossible to tear. This is particularly important when paired with a heavy-duty exterior fabric like 1050 Ballistic nylon: the seam joining exterior fabric to lining fabric can be a relatively weak point if the two fabrics have disparate tensile strengths.
210d nylon with an UHMWPE ripstop grid has become our go-to lining fabric.
Halcyon 400 denier is the big brother of our Halcyon 200 denier, and in a way, a cousin to 420HT Parapack. Made for us in Japan, it's a ripstop fabric woven of 400 denier nylon (base fabric) with a square grid of 420 denier UHMWPE (ultra-high-molecular-weight polyethylene) yarns every .25" / 6mm. UHMWPE is one of the strongest fibers known to man, and is almost impossible to tear.
Halcyon 400d is similar in feel and weight to our 420HT Parapack, though with its grid of UHMWPE, its appearance is somewhat more modern or "technical". And while the base material is not 6,6 nylon, it is still considered to be "high tenacity"; without the UHMWPE grid, the base fabric is what most of the world's automotive airbags are made of.
Because of its remarkable tear strength and very good abrasion resistance, Halcyon 400d is an excellent choice as a lighter-weight alternative to 1050d ballistic nylon for travel bags and backpacks. Note that at the end of the day, the base fabric is only about one-half the thickness of 1050d ballistic nylon, and you'll need to treat your Halcyon 400d bag with a bit of respect: no kicking your bag along the floor at the airport, or tossing it from a moving vehicle. That said, the ripstop grid of UHMWPE makes it very difficult to cut or tear, and will tend to foil most attempts at slash-and-run theft.
Our Halcyon 400d is available both with the conventional white (undyed) UHMWPE grid, as well as a black (actually very dark grey) UHMWPE grid. Either way, we think this is a handsome as well as supremely functional fabric.
Meshes and Knits
There's a huge variety of knit fabrics and meshes used in the bag and backpack industry. Open- and closed-cell foam can be laminated to stable warp knits and stretchy Raschel knits of polyester, nylon, and nylon/lycra blends to create composite materials with unique properties.
Brushed polyester tricot laminated to soft open-cell foam provides good protection for electronics with very little weight.
Polyester and nylon meshes lend visibility to a bag's pockets and breathability to surfaces that make contact with the user: 3D Aerospacer Mesh is a polyester/nylon blend that can help transport moisture and heat away from the contact areas on the panel against your back.
420d HT nylon Classic Parapack
420 denier, high tenacity, type 6,6 nylon fabric (Parapack) was originally developed for the military for use in parachute backpacks—the thing on the guy’s back that holds the parachute. Paratroopers needed a fabric that was smooth and wouldn't hang up on anything as they jumped from the plane; it had to be light (obviously); and it needed to be strong so as not to be easily punctured or abraded.
You can think of 420 denier Parapack fabric as the little brother of 1050 denier Ballistic. Like 1050 Ballistic, 420 Parapack fabric is densely woven of high tenacity, filament nylon yarns. Both are also type 6,6 nylon, as opposed to the more common type 6. Type 6,6 has greater tensile strength than type 6, and very importantly type 6,6's melting temperature is higher by 40°C (70°F). This is a very good thing because the degradation of a fabric caused by abrasion is largely the result of heat building up during abrasion and damaging the material. A higher melting point means better abrasion resistance.
Like 1050 HT Ballistic cloth, 420d HT Parapack is relatively hard to dye and can sometimes have a heathery appearance.
Also like 1050d HT Ballistic, it's a filament fabric (as opposed to texturized) and tends not to accumulate snow, lint, or pet hair.
We got reacquainted with 420d Parapack back in 2013 as we developed the retro-inspired Guide's Pack and Founder's Briefcase. It has a great hand, a dense weave, and a less sparkly appearance than its cheaper imported cousins. We love it!
Nylon thread stretches with nylon fabric, and that's a good thing for final assembly seams and high stress areas. However, nylon thread requires an added binding agent (typically synthetic wax) to make it sewable. This wax often oxidizes (whitens) as it ages, which makes the thread stand out against the fabric, especially black thread on black fabric.
Polyester thread is excellent for exterior stitching because it fares better than nylon when exposed to sunlight, and produces a slightly neater stitch. Lacking the binding agent that nylon thread requires, its color remains stable over time.
Both nylon and polyester thread are available in different nominal sizes or weight; the bigger the number, the thicker the thread. In general, two rows of thinner thread are better than a single row of thicker thread, as one row can fail and the seam will still remain intact and functional.
We use different weights depending on the needed strength: nominally Tex 40 (pre-assembly over-lock); Tex 60 (labels, zippers and exterior top-stitching); Tex 70 and Tex 80 (final assembly, bar-tacking, etc.).
Our thread is made both in the U.S.A and in Germany. Like all of our components, we buy the best regardless of price.
Finally, seam failure in our bags is almost unheard of: properly stitched, the actual sewing is stronger than the fabric, the zippers and the buckles. If any thread or stitching on your TOM BIHN bag ever fails, we've almost certainly done something wrong, and we will fix it or replace it free of charge.
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.
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!