The birth of the slide fastener
The development of the ubiquitous zipper was a challenge to overcome continuing shortcomings.
Modern boots – and occasionally shoes – often rely on a slide fastener (‘zip’ or ‘zipper’) to secure them to the wearer’s foot. Of course, before this method was invented, other fastening system were used, such as laces, buckles and straps, and buttons.
The creativity which led to the modern slide fastener was a long process that involved several different people and a considerable period of time, which is an evolution that is common with many products we now take for granted. At the outset, Elias Howe (1819-1867), the American inventor of the lockstitch sewing machine, received a patent in 1851 for what was called an ‘automatic, continuous clothing closure’, which was more like an elaborate drawstring than a true slide fastener. However, being busy marketing his stitching machine at the time meant that his slide fastener design was shelved.
Over 40 years later, Chicago-born Whitcomb Judson improved Howe’s idea and began to market what he called a ‘Clasp Locker’, which was specifically designed for shoes. Judson also invented production machinery that made the Clasp Locker an inexpensive component.
The Judson Clasp Locker has been described as a complicated fastener featuring hooks and eyes led by a guide to close an item. Judson initially applied for a patent for his slide fastener in November 1891. At the time, the United States Patent Office did not require sight of a working model of an invention – it merely had to be a novel idea. Nevertheless, his creation was reportedly almost rejected by a patent assistant examiner because several other types of shoe fasteners had already been accepted. Not willing to risk his invention being refused a patent, Judson immediately set out to improve its design. He made a second application for an improved version some nine months later, while the first design was still being considered, and was granted two approvals on the same day in August 1893 – numbers 504,037: ‘Shoe Fastening’ and 504,038: ‘Clasp Locker or Unlocker for Shoes’. In order to manufacture his new device, Judson founded the Universal Fastener Company in Chicago in 1893. The product was launched at the 1893 Chicago World’s Fair, but failed to capture the public’s imagination Judson had obviously hoped for, and so at first met with little commercial success.
A new design
Within a short time, Judson had totally redesigned his slide fastener. US patent number 557,207: ‘Fastening for Shoes’, granted in March 1896, describes the updated invention with the following words: ‘...each link of each chain is provided both with a male and female coupling part, and when the chains are coupled together the female part of each link on one chain is engaged by the male part of a link on the other chain.’
In his patent application, Judson hinted at one of the reasons for his invention – an attempt to relieve the tedium of fastening high buttoned boots that were fashionable at the time. He wrote: ‘…it must be obvious that a shoe equipped with my device has all the advantages peculiar to a lace-shoe, while at the same time it is free from the annoyances hitherto incidental to lace-shoes on account of the lacing and unlacing required every time the shoes were put on or taken off the feet and on account of the lacing-strings coming untied. With my device, the lacing-strings may be adjusted from time to time to take up the slack in the shoes, and the shoes may be fastened or loosened more quickly than any other form of shoe hitherto devised, so far as I am aware.’
Unfortunately, Judson’s slide fastener was far from perfect, as it tended to break open without warning. In fact, while his ‘C-curity Clasp Locker’ (launched in 1905) was an improvement over his previous designs, it is said to have still exhibited this quite serious problem.
A fresh viewpoint
In 1906, 26-year-old Swedish-American electrical engineer Gideon Sundbäck was recruited to work for Whitcomb Judson’s Universal Fastener Company after it had relocated to Hoboken, New Jersey. Having sound technical skills (and helped undoubtedly by his marrying the plant manager’s daughter) soon led Sundbäck to promotion as the company’s head designer.
Between 1906 and 1914, Sundbäck made several improvements to the Universal Fastener Company’s slide fastener offerings. For example, he was responsible for refining the C-curity product which was still using a hook-and-eye system. Sundbäck’s improved version was called the ‘Plako’, but it also pulled apart too easily. As a result, it was no more successful than the previous versions. In 1913, he finally solved this problem, after radically moving away from the hook-and-eye principle. In his ‘Hookless Fastener No.1’, Sundbäck increased the number of fastening elements per inch from four to ten or eleven. His design featured two facing rows of teeth that were pulled into a single piece by a slider, while also increasing the opening for the teeth.
During the following year, Sundbäck developed a system called the ‘Hookless Fastener No.2’, which used interlocking teeth. In this design, each of the teeth was punched to form a conical projection on its top and a dimple on its bottom surface. The teeth on one side of the fastener were offset from those on the other side. Therefore, when the two strips of teeth were brought together by the ‘Y’ channels of a slider, the projection on top of one tooth engaged in the matching dimple in the bottom of the opposing tooth. Once the teeth were meshed together, there was insufficient movement to allow them to pull apart, thus solving the fault that had plagued the previous designs.
Sundbäck’s patent application for the ‘Separable Fastener’ was filed on August 27th 1914 and issued a little under three years later. For the first time, a product like a modern slide fastener had become a working reality. Obviously, a successful product needs an efficient method of production, so the inventor also created a machine which cut scoops from a special Y-shaped wire, punched the dimple and projection, and made a continuous chain by clamping each scoop onto a cloth tape.
Onomatopoeia at play
When did these slide fasteners become known as ‘zippers’? According to popular legend it was in 1923, when the US-based manufacturing company BF Goodrich fitted them to their rubber-based footwear – with the finished products being called ‘Zippers’ rather than the word simply referring to the closing device. Apparently, someone in the company thought it would be a good idea to market them after the sound they made when opened or closed quickly.
Over the years since the 1917 patent, various refinements have been made to Sundbäck’s toothed design, but today’s slide fasteners remain fundamentally the same. In addition to footwear, garments, bags, tents and a host of other consumer products, these components have found a number of exotic applications. These include airtight versions developed by NASA for high-altitude pressure suits and space suits – being capable of retaining internal air pressure in the vacuum of space (and also used on hazmat suits) – as well as watertight slide fasteners fitted to scuba diving dry suits and ocean survival outfits.
Throughout the centuries, many inventors have passed into history without receiving the accolade they deserved. This was not the case with Gideon Sundbäck, who was awarded a Gold Medal by the Royal Swedish Academy of Engineering Sciences in 1951, three years before his death.
This article was originally published on page 40 of the November 2020 issue of SATRA Bulletin.