Why Do Backpack and Tent Zippers Fail?

Why do Backpack and Tent Zippers Fail?

There are several kinds of zippers used on backpacks, tents, and outdoor apparel. Vislon zippers are made from molded plastic and are commonly found on apparel. Coil zippers have two coils that look like teeth, which are sewn to separate pieces of zipper tape. Coil zippers are mainly used on backpacks and tents because they are flexible and can flow along a curved seam or shape. A metal slider is used to force the two separate sides of the teeth together or apart.

Coil zippers are malleable, meaning they can bend into shapes, such as the curve of a rainbow tent door or a backpack pocket. When tiny debris such as sand becomes lodged in the coil, it will deform slightly when zipping or unzipping to accommodate the debris without jamming or pulling apart. This malleability or “self-healing” characteristic is the main reason coil zippers are used for outdoor applications such as backpacks and tents. But malleability has its limit, and coil zippers can fail in a variety of ways.

A Coil zipper, the type most commonly found on backpacks and tents.
A Coil zipper, the type most commonly found on backpacks and tents.

There are many zipper brands, but YKK is the most popular and very widely used for backpacks and tents. Below I discuss the best applications for different zipper sizes, different coil zipper types, how to maintain them, and how they can fail.

Zipper Sizes

If you look on the end or the back of the zipper slider nearest you, you will probably see a number; this indicates the size of the zipper. The numbers (#3, #5, #8, and so on) are based on a rough estimate of the width of the two sides of the coil when the teeth are locked together and the zipper is closed.

Sizes have changed over the years so an older #5 zipper may say “#5C” on the slider, whereas a new one might say “#5CN” or #5NO”. While all of these are very similar in size, they are not the same, and therefore not compatible with one another. But don’t fret, understanding these eccentricities only comes into play when swapping out a slider, which I’ll explain later.

#3 zippers work well for inner tents where fabric tension is low.
#3 zippers work well for inner tents where fabric tension is low.

It’s far more important to know that the most common sizes of zippers found on backpacks and tents are #3, #4.5, #5, #8, and #10. The bigger the number, the heavier the zipper will be. Low tension closures, such as the bug netting on tent doors, can often get away with #3 coil zippers, while higher tension closures, such as tent fly doors, often need a heavier zipper such as a #5 or #8. Problems arise when manufacturers use small zippers for high-tension applications.

A #5 water-resistant zipper on the Durston X-Mid 2P.
A #5 water-resistant zipper on the rainfly of the Durston X-Mid 2P.

Separating vs Non-separating Zippers

Separating zippers are usually found on apparel and sometimes on mummy bags. They allow the two sides of a jacket or sleeping bag to separate completely.

Non-separating zippers, on the other hand, are sewn together at one or both ends so they don’t come apart completely. They’re often used for tent fly doorways,

Waterproof and Water-resistant Zippers

YKK makes a water-resistant Uretek or Aquaguard coil zipper. The zipper tape is waterproof on the non-coil side of this zipper, with the two edges of the glossy, waterproof material coming flush together when the zipper is closed. Some manufacturers advertise these zippers as waterproof while others say they’re water-resistant. Because grains of sand, other debris, worn-out sliders, and high tension can easily create a gap between the two waterproof sides, I think it’s safe to assume these zippers are highly water-resistant and not waterproof. Tents such as the Mountain Laurel Designs Duomid and the Durston Gear X-Mid 1P use them.

Waterproof zippers do exist but they are not usually found on tents or sleeping bags. An example is YKK’s Proseal zipper which is used for drysuits and diving suits since it is both airtight and watertight.

Coil zippers are often found on backpack pockets such as this pocket on the Hanchor Marl
Coil zippers are often found on backpack pockets such as this pocket on the Hanchor Marl Backpack.

How to clean and maintain zippers

Zippers have a tendency to trap sand and other tiny debris between the teeth so it is a good idea to clean zippers regularly, especially when backpacking in sandy areas. Sand can jam zippers to the point that the slider won’t move back and forth along the coil. It can also keep the teeth from coming together completely so they come apart under moderate tension.

Over time, debris caught in the coil can wear down the metal slider. I know it’s counterintuitive, but the metal of the slider will grind down long before the plastic of the coil. This is due to the static nature of the slider vs the malleable nature of the coil. For this reason, tents and backpacks with multiple sliders on each zipper will last longer than those with only one slider. The coil will wear out eventually, with grit grinding up the teeth and fraying the thread that attaches the coil to the tape, but this will happen long after the slider wears out.

If you want to make your sliders and coil zippers last, clean your zippers after trips using Gear Aid Zipper Cleaner and Lubricant or soap, water, and a toothbrush. The benefit to using Gear Aid Zipper Cleaner and Lubricant is that it adds a protective finish to the coil that resists debris. Other dry lubricants such as silicone spray also help zippers slide smoothly and resist grit. Never use a wet lube such as olive oil, bacon fat, or WD-40 on your zipper. It will attract dirt, making things worse rather than better. Much worse.

If and when your tent zippers start separating every time you try and escape from the bugs, you will need to replace the slider. First, contact the manufacturer to see if they will send you a new slider. If they won’t, check the end or the back of the slider to identify the size and brand of your slider and order a few extras from a company like Ripstop By The Roll. Then, clip the coil, slide the old slider off, slide the new one on, and then repair the broken coil with a zipper stop, which can also be found where you get your sliders.

This #5 zipper is the right choice for this DCF tent fly where fabric tension will be high
This #5 zipper is the right choice for this DCF tent fly where fabric tension will be high.

How long should a coil zipper last?

The longevity of a coil zipper varies widely but is determined by the number of days the user used it, the types of environments in which it has been used (mountains vs beach vs desert), and the size of the zipper chosen for the particular application.

So, in theory, a tent manufactured with proper zippers (#3 for the inner and #5 for the fly), used primarily in non-sandy alpine environments, and cleaned regularly, won’t need a slider replacement for up to five years. The same tent used in filthy desert environments could need a slider replacement once a year. If this tent is made with a high tension fabric such as DCF, a slider replacement will be more frequent.

Take-aways

There are several types of zippers, but coil zippers are usually used on backpacks and tents.

  1. Tent and backpack manufacturers don’t always use the right zipper for the job. Be wary of #3 zippers on tent fly doors, but embrace their use on netting.
  2. Cleaning zippers will increase their lifespan.
  3. Sandy environments decrease the lifespan of a zipper.

Finally, when a zipper fails on a tent or backpack that doesn’t mean the product is dead. You can replace the slider and keep using it.

About the author

Ben Kilbourne has been backpacking at least once a month every month for the last twelve years. His explorations have taken him all over the west, but especially the canyon country of the Colorado Plateau. The geography of the west has become familiar to him. He has developed a rudimentary understanding of its geology, and an awareness of the subtle changes in flora and fauna due to soil, elevation, aspect, and precipitation and how these elemental things interact with both ancient and modern humans. His experiences on the land, whether triumphant or thwarted by events either in or out of his control, have provided the foundation for the work he does. Find Ben’s paintings, songs, and essays here http://benkilbourne.com/.

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13 comments

  1. On an extended desert trip, I brought a little travel toothbrush to clean the coils of my tent zipper. A few years later, I found that nice little travel toothbrush in my gear box and forgot what it had been used for, so I packed it to clean my teeth. The bits of sand that were worked down into the bristles were invisible to me when I put the toothpaste on, but as soon as I started brushing—yuck! I’ll label that toothbrush with a piece of tape that clearly reads SAND from now on.

  2. Very informative – thank you.

  3. I have had many zipper failures and being comfortable sewing have just replaced the zipper on my sewing machine. Its a project to use a stitch ripper to cut it out, release all the loose threads, set the new zipper in place with pins and then sew it all. Your article is a REVELATION! Truly, the zipper will start to fail to close and all that is wrong is the slider?? Wow.

    Next zipper fail I’ll be going after the slider first to see if that cures the problem. Is the slider also the culprit when a zipper closes, but then will pull open below the slider?

    I love my tents. Its almost romantic and I’ve felt that way since I was a boy and got my first canvas pup tent. The tent more than anything symbolizes adventure and freedom. Its no wonder that I love to care for them also. You didn’t mention post trip cleaning so I will. A setup and interior vacuum and wipe down doesn’t take long. Getting dirt out of and off of the tent means it can’t wear down floors and grind zippers. Running that vacuum over the zipper several times may dislodge embedded debris.

    Post trip setup and cleaning in my living room has revealed minor damage I’d not noticed, and its much more fun to repair at leisure, inside, than on the trail when it becomes major damage. Thanks for a truly informative article.

  4. Good article, thank you Ben. Another option if a coil zipper is separating and not closing the teeth is to carefully close the “mouth” of the slider slightly. VERY SLIGHTLY, using needle nose pliers on the front and the back sides of slider mouth (narrow part of slider). Do it very slightly and repeat with slightly more pressure if that didn’t solve problem. This can sometimes repair a coil zipper that is not closing the teeth. This is easier than replacing slider, and can be done in field, but slider replacement still might be needed. Fixed my tent this way in field with my mini multi-tool. Below is a YouTube link demonstrating it.
    https://m.youtube.com/watch?v=vpDbUFKaUyY

    • Last year I used the procedure bmcf described and it worked. Strongly agree with the suggestion to be very careful about how much pressure is used with the needle nose pliers. Have used the tent about a dozen times since the repair and the zipper still works fine. Before I used this repair procedure I borrowed a FixnZip repair device from another hiker while out on the trail. At the end of the hike he wanted his FixnZip back. When I got home I did a web search and found the same YouTube link included in bmcf’s post.

    • I have field repaired zippers the same way. Now, if I could always remember to zip up my fly…

  5. A bar of soap run along the zipper teeth/coil makes an excellent field repair. It’s also a pretty decent dry lube on it’s own.

  6. Somewhere along the line, maybe in boy scouts, I learned to use a candle to dry lube zippers by rubbing on the teeth to transfer the wax- I keep the “ends” of used-up candles for this purpose and it works great!

  7. Rather than commercial zipper stop I prefer using heavy duty “button & carpet thread” to sew a thick and more permanent zipper stop.

    I’ve found that over-tensioning a fly on teh zipper side is asking for trouble. Live and learn.

  8. Being a bee keeper in the pass i have saved bee wax and melted it down into small blocks. They work great as a lubricant for zippers.

  9. zip tip from the SeaCowboy Surfer… lube your zips with crayons. Yes, simple crayola crayons are great for zip lube… use it on surf bags being tossed in the sand everyday. Every Wave, Every Ride… the SeaCowboy :)

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