For a long time, I have been intrigued by the zipper. It is everywhere: on clothes, backpacks, shoes, sporting goods, suitcases, camping equipment, etc. But look at one closely and try to imagine how it works.

The basic principle is quite simple; two parallel chains of projections (teeth) lock and unlock to form a quick, easy, reliable means of opening and closing things. The chains of teeth are part of a truly ingeniously designed and engineered piece of precision equipment.

Given its ubiquity and generally flawless performance in so many everyday tasks, I believe the zipper truly deserves a place of honor on my list of what I like to call “extraordinary ordinary things.”

A Short History of Clothes Fasteners

Although it has numerous other applications, the primary function of the zipper is as a clothes fastener, i.e. to ease putting on and taking off wearing apparel.

As previously mentioned, because of the need for precision design and manufacture, the zipper is a rather recent development in the history of clothes fasteners—the number of which is eye-watering.

The fact is, for most of human history, clothes fasteners of any kind were not really used. They were not really needed because most clothing was in the form of tunic-like garments that were simply slipped over the head. The only thing that might have been necessary was something to close the hole through which the head was pushed if it was too voluminous for comfortable wearing.  

When clothing became more sophisticated, the ways and means of opening and closing garments became increasingly necessary. Devices for opening and closing garments used down the ages included, and to a large extent still include, the following.

• Broaches  

An early solution to the problem of an uncomfortably large neck hole on a tunic-like garment was the “‘keyhole opening,” a sort of round neckline with a slit in front. Once the head passed through, small brooches were used to fasten the edges of the slit together. Not surprisingly, the wealthier the person, the more ornate the brooch. Bigger brooches were used for cloaks and other more loosely-fitting garments.

• Buttons

Buttons probably developed from decoratively applied beads before being seen as something functional. Their transformation into clothes fasteners seems to have begun during the 9th century in Hungary, with their transformation into a combination of buttons and buttonholes probably emerged in the 13th century in Germany. Buttonholes had to be carefully handstitched with strong thread or cord for strength.

• Hooks and eyes

Hooks and eyes were used on late medieval garments to close collars, livery coats, and gowns. Fabrics with ornate patterns being popular in the latter part of the 15th century, a closure device that would not detract from those patterns was highly appreciated. Later they were used to close jerkins, gowns, jackets, and bodices.

Hooks and eyes are still very much in use today, predominantly on items of lingerie.

• Laces

Laces are strips of fabric used to hold garments together. Some of the earliest laced garments are believed to date back to the 12th century. Dresses of the period were laced at the sides through hand-sewn eyelets using a plaited or woven cord.

The same method was used in the late medieval period (from the 14th century onward) to open and close gowns and kirtles. Sometimes called a cotte, a kirtle was a type of garment worn by men and women. These were laced either at the sides or at the front or back.

• Toggles

Toggles are a form of button prominently used in medieval times on medieval shoes. In later centuries, toggles went out of fashion, being replaced on shoes by buckles, buttons, and laces.

These descriptions only graze the surface. Under each classification (and others not mentioned) there are so many subcategories and variations as to boggle the mind.

How the Zipper Works

A simple description of a zipper would look something like this:

A zipper (or “zip”) is a device consisting of two rows of teeth that can be made to interlock, thus tightly linking the two rows one to the other. When the two rows of teeth are not linked, the device is said to be “open”; when they are linked, the device is said to be “closed.” Opening and closing are carried out by a small element called a “slider” placed between the two rows of teeth. The slider is moved back and forth along the rows of teeth. A Y-shaped channel inside the slider meshes (interlocks) or separates (unlocks) the opposing rows of teeth, depending on the direction the slider is moved.  The slider bends the zipper slightly to open up the space and allow the opposite teeth to slide into their places.

The principal purpose of a zipper is to join two separate pieces of material (cloth, leather, plastic, etc.) so that they act as a single piece. For example, the zipper on a sports sack, wallet, purse, etc. is used to open and close the item.

There are numerous types of zippers to achieve this purpose; however, they may broadly be divided into two fundamental categories:

• Zippers that open only at one end, such as on a suitcase, briefcase, sports bag, shoes, etc.
• Zippers that open and close at both ends, such as on a jacket, blouse, vest, professional work clothes, etc.

The two categories have many parts in common; however, zippers that open and close at both ends have a few parts that zippers that open and close at only one end do not. Here are the key parts of zippers that open and close at both ends.

1. Top tape extension. The fabric part of the zipper that extends beyond the two chains of teeth, used to affix the device to the object to be opened and closed.
2. Slider. The V-shaped part of the zipper through which the two rows of teeth pass in order for them to lock (engage) and unlock (disengage), i.e. to open and close.
3. Top stops. Two pieces affixed to the top end of the zipper prevent the slider from coming off the chain.
4. Pull tab (puller). The part of the slider the user holds to pull the slider back and forth, i.e. open and close the zipper.
5. Tape width. The width of the fabric on both sides of the zipper that attach it to clothing or other objects.
6. Chain (zipper teeth). The continuous piece formed when the two halves of the zipper mesh, i.e. when the zipper is closed.
7. Bottom stop. A device affixed to the bottom end of a zipper to prevent it from spontaneously opening.
8. Bottom tape extension. The fabric part of the zipper that extends beyond the teeth at the bottom of the chain.
9. Insertion pin. A small piece extending at the bottom of one row of teeth on an open zipper that is inserted into the bottom stop so that the two rows of teeth will join when the zipper is pulled up to close, and so that the two rows of teeth will fully separate when the zipper is down to open.
10. Retainer box (pin box). A device at the bottom of the zipper to correctly align the pin so that the open zipper can be easily and smoothly closed.
11. Reinforcement film. A strip of plastic fused to each half of the zipper to allow it to be electronically “welded” onto a garment or other item without need for laborious, time-consuming sewing or stitching.

Note: The terms “bottom” and “top” are somewhat misleading. They envision a zipper used vertically; however, a zipper can be used in any orientation, i.e. vertical, horizontal, oblique. So in general, bottom simply means the end where the pull tab is located when the device is open and top the end where the pull tab is located when the device is closed.

For illustrations of the two types of zippers, visit:  

https://www.aeempire.com/structure-of-zipper/

History of the Zipper

Like many other extraordinary ordinary things, the zipper became ubiquitous because of the Industrial Revolution, which began roughly near the end of the 1700s. This is because while the concept may be easy, the realization is high-tech. It is hard to imagine that anyone even conceived of the zipper before the Industrial Revolution.

The concept of the zipper is generally attributed to American inventor Elias Howe. Howe is best remembered for his invention of the modern sewing machine, for which he received a U.S. patent in 1846. In 1851, he was awarded a patent for a device he called an “automatic continuous clothing closure.” While functioning similarly to a modern zipper, Howe’s design was nonetheless considerably different. It operated as individual clasps that were manually joined and pulled shut by using a string. Despite having achieved a patent, Howe decided not to continue developing his invention.

It was more than 40 years later, in 1893, that fellow American Whitcomb L. Judson sought a patent for what he called a “clasp locker or unlocker for shoes.” This was essentially a guide (fastener, slider) used to close up the space between a shoe’s clasps on one side to attachments on the other. Being removable, the guide could be used both for pushing the bulky clasps down, then subsequently pulling them closed. The invention proved to be very difficult to produce and also time-consuming to use, and thus of no great benefit.

A second Whitcomb Judson patent, also granted in 1893, was a transition from the former bulky clasps to hooks and eyes. Called the C-curity (security), this device consisted of a series of loops (short metal extensions) that were manually laced into the boot or shoe. The improvement was significant because the device functioned as a unit instead of as individual clasps. However, it eventually proved to be unsatisfactory because of its tendency to spring open.

In 1912, Swedish-American engineer Gideon Sundback enhanced the previous zipper models with a device called the “Plako fastener.” Featuring an oval hook protruding from the tape to which they were attached, the Plako fastener provided a more secure fit than the C-curity and ensured a tighter fit. However, it proved to be insufficiently flexible; moreover, it failed to stay closed when it was bent.

In 1913, Sundback introduced a revised version of the Plako fastener. This model featured interlocking oval scoops (instead of the previously used hooks) that could be joined together tightly by a slider in a single movement. This final Sundback model is generally recognized as the first modern zipper.

In the early stages, modern zippers were used almost exclusively for boots and tobacco pouches. However, during the First World War (1914–1918), military and navy designers adapted the zipper to flying suits and money belts, helping to build the device’s reputation for durability.

The name Plako fastener used by Sundback on his patents seemed to have had little appeal to the general public. So in 1923, rubber manufacturer B.F. Goodrich, which was producing rubber boots and galoshes using the device, gave it the onomatopoeic name “zipper” after the “zip” sound the slider made when being pulled up and down. And the name stuck, not only in English but in a number of other languages as well.

While the zipper’s fundamental design has remained largely unchanged for over a century, the range of zippers has continued to expand.

Originally, zippers were designed for use in heavyweight or thick materials, and thus produced in metals. Made in aluminum, brass, and nickel, these metal zippers were eventually incorporated into everyday wearing apparel such as denim jeans. The success of zippers grew as designers experimented with producing them in materials other than metal, such as plastic zippers, which are soft, pliable, and easy to maintain. Today, zippers are available in a wide variety of materials for a wide variety of uses ranging from utilitarian to aesthetic (fashion).

How to Fix a Jammed Zipper

We have all had the problem at one time or another. When being pulled up or down, the zipper jams and will move no farther. Sometimes brute force can be used to unjam it, but this is seldom the case. So, what to do? There are several methods for unjamming a zipper. This problem is so common that today entire websites are devoted to helping people unjam zippers.

If the slider is stuck and won’t move, the most common reason is that something has become wedged in the teeth or caught in the slider. This will most likely be a bit of fabric or thread.  To check for this, turn the piece of clothing or bag inside out and follow along the zipper lines to see if there is anything there you can remove by tugging it away. If there is a thread or piece of fabric you cannot get hold of with your fingers, try using a pair of tweezers to pull it away.

If it is still hard to move the zipper after removing the obstruction, use a graphite pencil to run lead all over the zipper (front and back) a few centimeters above and below the slider. This will lubricate the teeth and should help the zipper to run free.

If it is still well and truly jammed, there are several household items that can be used as a lubricant, including baby powder, talcum powder, lip balm, Vaseline, bar soap, glass cleaner, wax paper, etc. Be certain to choose a lubricant that will not stain the fabric around the zipper you are trying to unjam. Apply the lubricant in the same way as you would a graphite pencil. Then give the slider a tug and it should move as good as new.

A number of other problems can arise with zippers. They are rare, but they do happen. For example, the zipper won’t stay up, the teeth won’t close, the pull tab breaks off, etc. There are numerous websites ready and willing to help you with a disabled zipper. To find them, type “how to fix a broken zipper” into any search engine and take your pick.

The Zipper in Culture

In many of these “extraordinary ordinary things” blogs, I have included a section on how the item in question is reflected in culture. Surprisingly, the zipper seems to have had very little cultural impact. I have been able to find essentially no significant reference to the zipper in the titles and/or plots of novels and plays, in the titles and/or texts of poems, paintings, prescient quotations, etc.

Popular music appears to be somewhat of an exception. There is a genre of music called a zipper song. This is a song in which each verse is essentially the same as the preceding one with only a word deleted and a different word “zipped in” to significantly change the verse’s meaning.

The word “zip” does often appear in the title or lyrics of many popular songs, but usually in terms of the zip sound, not as a reference to the zipper as a fastener. For example: “Zip-a-dee-doo-dah, zip-a-dee-ay/My, oh, my, what a wonderful day/Plenty of sunshine headin’ my way/Zip-a-dee-doo-dah, zip-a-dee-ay!” Songs that do refer to the zipper as a fastening device are rather rare, some of which probably shouldn’t be sung in polite company.

ZIP Code

In the United States, the word ZIP has taken on a very special significance. “ZIP code” is the  American term for a postal code to designate a very specific way of sorting and delivering mail.

ZIP is an acronym for Zone Improvement Plan. The term was chosen by the U.S. Postal Service to suggest that with the system mail travels more swiftly and efficiently to its destination. In English, the expression “to zip along” means to move quickly.

Introduced in 1963, the basic format consisted of five digits. In 1983, an extended ZIP+4 code was introduced which includes the five digits of the ZIP code followed by a hyphen and four digits that designate a more specific location.

Jokes

There are many jokes and wry quotations related to the zipper; however, they must be handled with care. In many people’s minds, the word zipper is intimately associated with the opening and closing device on the front of men’s trousers, such that most quips about zippers seem to be infused with sexual innuendo, i.e. they are rather off-color. Here are a few (very few) that are worth a look and are unlikely to cause discomfort or offense.

“First you forget names, then you forget faces. Next, you forget to pull your zipper up. And finally, you forget to pull it down.”—George Burns

“Nobody notices it when your zipper is up, but everyone notices when it is down.”—Cynthia Lewis

“I don’t want to see the zipper in the back of the monster suit. Like everybody else who goes to the movies, I want to believe the monster is real.”—Eric Stoltz

“To think, we have the garment industry instead of nature to thank for the zipper concept when it would have come in so handy for childbirth.”—Jane Wagner

“I’ve no time for broads (women) who want to rule the world alone. Without men, who’d do up the zipper on the back of your dress?”—Mae West

Zipper and Computers

To serious users of computers (computer scientists, programmers, academics, business people, civil servants, etc.), the term “zip” represents a well-known and highly appreciated computer facility.

Specifically, the zip command in a computer’s operating system does two things. It gathers a set of files that are in a folder into an archive, which is a file that strings them all together with separator markers. It compresses that file by substituting a short code for frequently appearing substrings in the file and appends the coding table at the end so that the recipient can run the process in reverse and recover the original file. Creating a zip file typically compresses files to 50–85 percent of their original size. The amount of compression depends on how many repeating substrings are in the file. Text usually compresses more than images.

The resulting zip file can be sent as a single email attachment rather than individually attaching say 5, 10, 15, 20, etc. documents and images. Likewise, the receiver does not have to painstakingly download each individual attachment, but rather only a single zip file. This can then be simply and virtually instantaneously decompressed into the original folder and all its individual files. Thus, considerable time is saved by both the sender and the receiver.

As suggested above, the technical and practical benefits of this facility are appreciable.

Technical

Because a zip file has been compressed, it takes up less space in memory. Given the huge amount of storage available in modern computers, this no longer has the importance it once did. Nevertheless, waste of memory is a waste of potential, i.e. as the proverb reminds us “waste not, want not.”

Practical

Being compressed, a zip file can more easily and rapidly be transferred via the internet or local networks from one computer to another. Zip compression can sometimes be of considerable help for sending mail across a mail system with a length limit on attachments. For example, suppose the system limits attachments to a maximum of 10MB. Compressing the attachment to 85 percent of the original size means that the sent file could be the equivalent of 11.7 MB (10 MB/0.85). Compressing the attachment to 50 percent of the original size would mean that the sent file could be the equivalent of  20MB (10MB/0.50). 

Another very practical aspect of compression is, as noted earlier, the ability to zip a folder (directory) into a single zip file.

Several computer techniques use the term “zip” or “zipper” because they are fast and collect data elements into a bundle.  These include:

• Zipper data structure (shown as graphs), which represents tree hierarchies of many data structures with paths that allow rapid traversal and update of the structure.  A “tree” can be seen as a set of paths from the root to each leaf.
• Zipper logic, a graph rewrite system that modifies zipper graphs
• Zipper CMOS, a dynamic CMOS circuit technique that also provides protection against instability and charge-sharing problems.

Another zipper term that has not yet gained currency, but probably should, is inspired by recent dramatic and crippling attacks on the computers of major businesses, associations, and even national security installations.

During World War II, to protect warships and supply ships on the high seas from attack due to naval personnel inadvertently giving clues to their location, a common mantra was: “Loose lips sink ships.” These five words saved countless lives and helped bring the world’s most devastating conflict to an end. To protect against attacks and disruption of vital computer-based facilities (with possibly lethal consequences), today this is often replaced by an even shorter mantra: “zip your lip.”