{
  "patent_number": "US 2929804",
  "country": "US",
  "title": "How Spandex Elastic Fibers Are Chemically Engineered",
  "original_title": "Elastic filaments of linear segmented polymers",
  "summary": "DuPont's 1960 patent for a stretchy, durable synthetic fiber made from segmented polymers, which became the foundation for modern Spandex.",
  "what_it_does": "The patent describes a synthetic filament that combines high elasticity with durability. It achieves this by using a segmented copolymer structure, specifically alternating soft ether segments for stretch and hard urea/urethane segments for strength. The claim defines the material by its physical performance: it must recover more than 90% of its original length after being stretched and maintain its tension (low stress decay) over time. This specific chemical arrangement allows the fiber to act like rubber but remain stable at temperatures above 150 degrees Celsius.",
  "what_it_does_not_cover": [
    "Does not cover non-segmented polymers or simple rubber-based elastic materials.",
    "Does not cover fibers that exhibit high stress decay (losing tension quickly) above 20%.",
    "Does not cover polymers with an inherent viscosity below 1.0, as these lack sufficient molecular weight for fiber formation."
  ],
  "filed": "1955-01-31",
  "granted": "1960-03-22",
  "expires": "1977-03-22",
  "status": "expired",
  "holder": "EI Du Pont de Nemours and Co",
  "holder_url": "https://patentbrief.org/company/ei-du-pont-de-nemours-and-co",
  "inventors": [
    {
      "name": "Steuber Walter",
      "url": "https://patentbrief.org/inventor/steuber-walter"
    }
  ],
  "times_cited": 71,
  "tags": [
    "materials",
    "consumer_electronics"
  ],
  "abstract": null,
  "url": "https://patentbrief.org/patent/us/2929804/spandex-lycra-elastic-fiber",
  "markdown_url": "https://patentbrief.org/patent/us/2929804/spandex-lycra-elastic-fiber/md",
  "google_patents_url": "https://patents.google.com/patent/US2929804",
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}