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've mostly transitioned from utilizing YKK® Aquaguard® water-repellent zipper in favor of YKK® Racquet Coil zippers with a water repellent treatment. To learn more about that transition, check out this blog post: Zipper Updates. So this is actually two changes at once: the zipper itself is changing, and the way the zipper is made water repellent is changing as well.
Racquet Coil (RC) zippers are coil zippers that are engineered by YKK to be tough and resist abrasion. An RC zipper looks almost indistinguishable from the standard coil zippers we’ve been using for decades: our best guess is that none of you would have noticed the change had we not pointed it out. The subtle but important difference is that on a Racquet Coil zipper, the thread that holds the continuous coil (which creates the “teeth” of a coil zipper) is recessed below the surface of the plastic coil itself; this is achieved by making the coil somewhat oblique in shape. Like a “racquet” in profile:
The second change is our moving away from the Aquaguard® urethane coating on the back side of zipper tape (the fabric part of a zipper) in favor of a durable water repellent (DWR) treatment on the tape of the Racquet Coil zipper. While folks have always appreciated how water repellent our bags are, some folks weren’t fans of how the Aquaguard® zippers require a little bit of an extra tug to open and close due to the thickness added to the zipper tape by that urethane coating. In our own tests, we found that the water repellency of the Racquet Coil zipper treated with DWR to be on par with that of the standard coil Aquaguard zippers. (Note that YKK applies the DWR to our Racquet Coil zipper on special order – Racquet Coil is not water repellent by nature.) And, since the Racquet Coil zippers are smoother to zip open and shut than Aquaguard®, the transition to Racquet Coil seemed like a no brainer to us. Some folks may still prefer Aquaguard®, some folks will be delighted by the transition to Racquet Coil, and probably most folks would appreciate either zipper, as both are high quality options.
Two bags that will continue to utilize an Aquaguard® zipper are the Synik 22 and Synik 30: that little bit of an extra tug that’s required to open Aquaguard® zippers is also what prevents the clamshell-style main compartment zipper of the Syniks from zipping itself fully option.
Below is some additional information about Aquaguard® that we’d thought we’d keep around, just in case folks find it useful:
Aquaguard zippers have a urethane coating on the flat side that makes it highly water repellent (though not waterproof). When we first started using them, we 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 could still see the glossy coating—you just needed to look inside the bag.
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; this is due to the fact that the same urethane coating that makes the zipper water-repellent 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.
As mentioned above, when Aquaguard® zippers were first introduced, everyone sewed them in upside down (or backwards, or “reverse”). Nowadays, 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 even particularly water repellent; a further complication is that there is now coated zipper chain available that is intended to look water repellent, but isn’t. An interesting side note: coil zippers are engineered to best bend around corners and curves when the teeth are on the outside of any curve, and so sewing any zipper that curves or bends in an up-side-down or reverse orientation will theoretically cause the zipper to wear out prematurely.
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!