page_title: Zipper
section_title: Air and water tightness
hierarchical_section_title: Zipper / Types / Air and water tightness
caption_attribution_description: Română: Fermoar etans la costumul de scafandru English: Dry suit zipper detail
context_page_description: A zipper, zip, fly, dingy, or zip fastener, formerly known as a clasp locker, is a commonly used device for binding the edges of an opening of fabric or other flexible material, such as on a garment or a bag. It is used in clothing, luggage and other bags, sporting goods, camping gear, and other items. Zippers come in all different sizes, shapes, and colors. Whitcomb L. Judson, who was an American inventor from Chicago, is sometimes given credit as the inventor of the zipper, but he never made a practical device. The method, still in use today, is based on interlocking teeth. Initially, it was titled the "hookless fastener" and was later redesigned to become more reliable.
context_section_description: Airtight zippers were first developed by NASA for making high-altitude pressure suits and later space suits, capable of retaining air pressure inside the suit in the vacuum of space.
  The airtight zipper is built like a standard toothed zipper, but with a waterproof sheeting (which is made of fabric-reinforced polyethylene and is bonded to the rest of the suit) wrapped around the outside of each row of zipper teeth. When the zipper is closed, the two facing sides of the plastic sheeting are squeezed tightly against one another (between the C-shaped clips) both above and below the zipper teeth, forming a double seal.
  This double-mated surface is good at retaining both vacuum and pressure, but the fit must be very tight, to press the surfaces together firmly. Consequently, these zippers are typically very stiff when zipped shut and have minimal flex or stretch. They are hard to open and close because the zipper anvil must bend apart teeth that are being held under tension. They can also be derailed (and damage the sealing surfaces) if the teeth are misaligned while straining to pull the zipper shut.
  These zippers are very common where airtight or watertight seals are needed, such as on scuba diving dry suits, ocean survival suits, and hazmat suits.
  A less common water-resistant zipper is similar in construction to a standard toothed zipper, but includes a molded plastic ridge seal similar to the mating surfaces on a ziploc bag. Such a zipper is easier to open and close than a clipped version, and the slider has a gap above the zipper teeth for separating the ridge seal. This seal is structurally weak against internal pressure, and can be separated by pressure within the sealed container pushing outward on the ridges, which simply flex and spread apart, potentially allowing air or liquid entry through the spread-open ridges. Ridge-sealed zippers are sometimes used on lower-cost surface dry suits.
caption: Waterproof zipper on a diving dry suit. The exterior metal segments clamp the waterproof sheeting over the concealed zipper teeth. The zipper teeth are not visible in this image (obscured by the edges of the waterproof sheet).
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