You can freely build on How Spandex Elastic Fibers Are Chemically Engineered
This patent expired in 1977. Every claim — 1 independent, 0 dependent — is now unenforceable. Anyone can use, reproduce, manufacture, sell, or offer for sale this technology without a license.
Original assignee
EI Du Pont de Nemours and Co
Patent granted
1960
Expired
1977
Forward citations
71
What this patent covers
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 is now free to use
All 1 claims of US 2929804 are in the public domain. Specifically:
Claim 1: A FILAMENT HAVING AN ELASTIC RECOVERY ABOVE ABOUT 90%, A STRESS DECAY BELOW ABOUT 20%, AND AN ESSENTIALLY LINEAR STRUCTURE OF A SEGMENTED UREA/URETHANE/ETHER COPOLYMER HAVING A POLYMER MELT TEMPERATURE ABOVE 150* C. AND AN INHERENT VISCOSITY OF AT LEAST 1 AS MEASURED IN A SOLUTION OF HEXAMETHYLPHOSPHORAMIDE HAVING A CONCENTRATION OF 0.5 GRAM PER 100 ML. OF SOLUTION, SAID COPOLYMER — 1 specific element
The 0 dependent claims add narrowing limitations and are also free.
What is NOT covered
Patent expiry frees this specific invention. Separately-patented improvements made after expiry may still be protected.
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.
Who is building on this today
The technology is now a commodity produced by major chemical manufacturers like The Lycra Company, Hyosung TNC, and various global textile suppliers. These companies continue to refine the polymer chemistry to improve moisture-wicking and heat-resistance properties.
Products built on expired version of this technology
Lycra brand spandex
Athletic compression leggings
Swimsuits
Elastic waistbands in denim
How to cite this patent in your documentation
EI Du Pont de Nemours and Co. US Patent 2929804. Elastic filaments of linear segmented polymers. Granted 1960, expired 1977. Now in the public domain.
Note: This is a convenience citation. Consult a patent attorney for formal freedom-to-operate analysis.
PatentBrief is an educational resource and does not provide legal advice. Patent expiration information is derived from USPTO records and may not reflect continuation patents, divisional filings, or separately-patented improvements. For commercial use or production decisions, obtain a formal freedom-to-operate (FTO) opinion from a registered patent attorney.