The Evolution, Manufacturing, and Quality Assurance of Modern Zippers

Background

Fasteners have evolved from bone and horn pins to today’s sophisticated zippers. Early closures—buckles, laces, safety pins, and buttons—were practical but cumbersome. Buttons with buttonholes remained essential, yet they posed challenges that drove the search for better solutions.

In 1851, Elias Howe, inventor of the sewing machine, introduced an “automatic continuous clothing closure.” Though ingenious, it never entered the market. The next milestone came in 1893 when Whitcomb L. Judson patented a slide fastener that combined hooks, eyes, and a clasp. After showcasing it at Chicago’s 1893 World’s Columbian Exposition, Judson secured funding from Lewis Walker, and together they founded the Universal Fastener Company in 1894.

Judson’s early zippers still resembled buttons, but by the late 1890s he developed a fully separable design and discovered that clamping teeth onto a sewn cloth tape—rather than embedding the teeth—yielded superior performance.

Despite progress, zippers still popped open and jammed until 1906, when Otto Frederick Gideon Sundback joined Judson’s company (then Automatic Hook and Eye Company). Sundback’s 1913 patent, Plako, is regarded as the birth of the modern zipper. His “Hookless Number One” featured jaws that clamped beads, quickly succeeded by “Hookless Number Two,” a design strikingly similar to today’s zippers. Nested, cup‑shaped teeth and a one‑process metal‑stamping machine made large‑scale production feasible.

World War I accelerated adoption: zippers were used on soldiers’ money belts, flight suits, and life vests. Wartime shortages pushed Sundback to create a machine that used only 40 % of the metal required by earlier designs.

Commercial production began in the 1920s when B. F. Goodrich ordered zippers for galoshes. Goodrich’s president, Bertram G. Work, coined the term zipper, though he preferred the technical name slide fastener.

World War II once again reshaped the industry. German factories were destroyed, and metal scarcity prompted West German Opti‑Werk GmbH to explore plastics. J. R. Ruhrman and associates secured a German patent for a plastic ladder chain, while Alden W. Hanson devised a method to sew a plastic coil into cloth tape in 1940. Independently, A. Gerbach and William Prym‑Wencie introduced a notched plastic wire that could be woven directly into fabric.

Sales climbed rapidly: 24,000 zippers sold in 1917, 60 million in 1934, and today billions are produced for everything from blue jeans to sleeping bags.

Raw Materials

The core components of a zipper are:

• Stringer: the tape and teeth assembly that constitutes one side of the zipper.
• Slider: the mechanism that opens and closes the zipper.
• Tab: the pull piece that moves the slider.
• Stops: devices that prevent the slider from leaving the chain.

Separating zippers use a box and a pin as dual stops when assembled.

Hardware materials vary:

• Metal: stainless steel, aluminum, brass, zinc, or nickel‑silver alloy. Steel zippers may be coated with brass or zinc, or painted to match the garment.
• Plastic: polyester or nylon for hardware; the slider and pull tab are typically steel or zinc.

Cloth tapes are made from cotton, polyester, or blends. Dual‑end zippers that open at both ends are reinforced with a strong cotton‑nylon blend to prevent fraying.

The Manufacturing Process

Modern zippers—whether metal or plastic—share core production steps. The following sections detail the methods for each material type.

Making Stringers – Metal Zippers

• 1. The classic Sundback process (1923) starts with a round wire rolled into a Y‑shape. The wire is sliced to create a tooth of appropriate width, then placed on a rotating turntable. A die punches a scoop shape into the tooth; the turntable rotates 90° to process the next tooth. After a second rotation, the first tooth is clamped onto the cloth tape, which is raised slightly to accommodate the opposing tooth. Although precise, this method is labor‑intensive.
• 2. A 1940s improvement uses a flattened wire that passes between a heading punch and a pocket punch to form scoops, followed by a blanking punch that shapes a Y. The Y’s legs clamp onto the cloth tape. This approach is faster and more efficient than Sundback’s original.
• 3. A molten‑metal technique molds a chain of teeth around the cloth tape. Molten zinc is injected under pressure; cooling releases the formed teeth, which are then trimmed.

Making Stringers – Plastic Zippers

• 1. Spiral plastic zippers can be produced by notching a round plastic wire, then feeding it between two heated screws rotating in opposite directions to form loops. A head maker forms a round knob at each loop’s front. Left and right spirals are created on separate machines to match upon assembly. An alternative single‑machine method loops wire twice between notches on a rotating wheel, simultaneously forming heads and producing two linked chains that can be sewn onto cloth tapes.
• 2. Toothed plastic zippers use a molding process similar to metal. A rotating wheel holds small molds shaped like flattened teeth; semi‑molten plastic is injected, then solidified. A folding machine bends the teeth into a U‑shape ready for sewing.
• 3. Ladder plastic zippers are made by winding plastic wire onto alternating spools on a rotating wheel. Strippers lift the loops, while a heading and notching wheel shapes the U‑shaped teeth and forms heads for sewing.
• 4. High‑quality garment zippers may weave plastic wire directly into the fabric using weaving techniques. This method is less common in the U.S. but frequently imported.

Completing the Manufacturing Process

• 7. After stringers are produced, they are temporarily joined with a slider‑like device, pressed, and for metal zippers, brushed to remove sharp edges. The tapes are starched, wrung, dried, and, for metal zippers, waxed to ensure smooth operation. All are wound onto large spools for later assembly.
• 8. Separately, sliders and pull tabs are stamped or die‑cast. The continuous zipper tape is unrolled; teeth are removed at intervals to create gaps for smaller chains. Bottom stops are clamped, sliders threaded onto chains, top stops added, and gaps cut at the midpoint. For separating zippers, gaps are reinforced with tape, then split. Finally, the slider, box, and pin are assembled onto their respective chains.
• 9. Completed zippers are stacked, boxed, and shipped to apparel, luggage, and other manufacturers, or directly to retailers for consumer purchase.

Quality Control

Zippers must deliver flawless performance in everyday use, which demands rigorous quality checks.

Manufacturers verify tolerances—width, length, tape end lengths, tooth dimensions, chain length, slide and stop dimensions—to ensure they fall within a 90‑99% acceptable range. Statistical sampling confirms batch consistency.

Flatness is tested by passing a gauge over the zipper; multiple contacts indicate a defect. Straightness is assessed by aligning the zipper against a straight edge.

Strength testing involves a tensile machine that pulls a tooth until it separates from the cloth, measuring the required force. Entire zipper pulls are tested similarly to gauge the force needed to separate the two halves. Compression tests identify failure points under pressure.

Ease of zipping is measured by the force required to operate the slider; garments require low force to prevent tearing, whereas mattress covers may tolerate higher forces.

Laundering durability is evaluated by washing the zipper in hot water, bleach, and abrasives, then agitating it with steel balls to assess coating abrasion.

Colorfastness is crucial for garments that will be dry‑cleaned or washed, ensuring the zipper tape retains its hue under care instructions.

Shrinkage is measured by marking the cloth tape, subjecting it to heat or wash, and recording the change in distance between marks. Heavy‑weight zippers should exhibit no shrinkage; lightweight zippers may shrink 1–4%.