# How Spandex Elastic Fibers Are Chemically Engineered

> DuPont's 1960 patent for a stretchy, durable synthetic fiber made from segmented polymers, which became the foundation for modern Spandex.

- **Patent:** US 2929804
- **Original title:** Elastic filaments of linear segmented polymers
- **Owner:** EI Du Pont de Nemours and Co
- **Granted:** 1960
- **Status:** Public domain (expired)
- **Times cited:** 71
- **Field:** materials, consumer_electronics

## 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.

## The clever bit

The innovation was the 'segmented' architecture: by alternating soft, flexible chains with rigid, interlocking chemical segments, the material mimics the properties of natural rubber without its tendency to degrade or lose shape.

## Real-world examples

1. Lycra brand spandex
2. Athletic compression leggings
3. Swimsuits
4. Elastic waistbands in denim

## Why it matters

This patent introduced the world to the chemistry of Spandex (Lycra). It enabled the mass production of garments that could stretch and snap back, fundamentally changing the design of athletic wear, swimwear, and intimate apparel.

## Frequently asked questions

### What does How Spandex Elastic Fibers Are Chemically Engineered cover?

DuPont's 1960 patent for a stretchy, durable synthetic fiber made from segmented polymers, which became the foundation for modern Spandex.

### Who owns patent US 2929804?

EI Du Pont de Nemours and Co owns this patent, granted in 1960.

### When does this patent expire?

This patent has expired and is now in the public domain — anyone can use the invention freely.

### What is patent US 2929804 cited by?

This patent has been cited by 71 later patents that build on its ideas.

### What problem does this patent solve?

This patent introduced the world to the chemistry of Spandex (Lycra). It enabled the mass production of garments that could stretch and snap back, fundamentally changing the design of athletic wear, swimwear, and intimate apparel.

### What does this patent NOT cover?

Does not cover non-segmented polymers or simple rubber-based elastic materials.

**Full plain-English explainer:** https://patentbrief.org/patent/us/2929804/spandex-lycra-elastic-fiber

**Original patent:** https://patents.google.com/patent/US2929804

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_Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._


## Related patents

Semantically similar inventions in the PatentBrief corpus:

- [How Wallace Carothers Invented Nylon](https://patentbrief.org/patent/us/2130523/nylon-polyamide-carothers) — The foundational 1935 patent for synthetic linear polyamides, the chemical process that created the material we now call nylon.
- [How Stephanie Kwolek Invented the Liquid Crystal Solution for Kevlar](https://patentbrief.org/patent/us/3671542/kevlar-aramid-fiber) — A 1969 chemical discovery describing a specialized liquid mixture that allows for the creation of incredibly strong, high-performance synthetic fibers.
- [The Molecular Structure of Kevlar High-Strength Fiber](https://patentbrief.org/patent/us/3819587/kevlar-aramid-fiber-kwolek) — Stephanie Kwolek's 1971 patent for DuPont describing the molecular alignment and manufacturing of extremely strong, lightweight synthetic aramid fibers, which became famous as Kevlar.
- [Making Strong, Porous PTFE: The Gore-Tex Process](https://patentbrief.org/patent/us/3953566/gore-tex-expanded-ptfe) — This patent describes a specific process for rapidly stretching a highly crystalline form of PTFE plastic to create a strong, porous material with a unique internal structure, forming the basis for products like Gore-Tex.
- [How DuPont Invented Neoprene Synthetic Rubber](https://patentbrief.org/patent/us/1967861/neoprene-synthetic-rubber) — A 1934 patent describing the chemical process to turn chlorobutadiene into a durable, oil-resistant synthetic rubber known as Neoprene.