# The Molecular Structure of Kevlar High-Strength Fiber > 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. - **Patent:** US 3819587 - **Original title:** Wholly aromatic carbocyclic polycarbonamide fiber having orientation angle of less than about 45{20 - **Owner:** EI Du Pont de Nemours and Co - **Granted:** 1974 - **Status:** Public domain (expired) - **Times cited:** 141 - **Field:** materials, aerospace, automotive ## What it does This patent claims a synthetic fiber made from aromatic polyamides (aramids) where the polymer chains are highly aligned. Specifically, the chain-extending bonds from each aromatic ring are coaxial or parallel and oppositely directed (para-oriented). This alignment is characterized by an 'orientation angle' of less than 45 degrees, meaning the polymer chains lie nearly parallel to the fiber axis. This tight alignment gives the fiber incredible tensile strength (tenacity of at least 5 grams per denier) and stiffness (initial modulus of at least 300 grams per denier). When spun from a liquid crystalline solution, the molecules line up like logs in a river, creating a fiber that is five times stronger than steel on an equal-weight basis. ## What it does NOT cover - Does not cover aliphatic polyamides like nylon, where the carbon chains are flexible and do not contain rigid aromatic rings. - Does not cover fibers with a high orientation angle (above 45 degrees), where the polymer chains are disorganized and lack high tensile strength. - Does not cover meta-oriented aramid fibers (like Nomex) where the chain bonds are not coaxial or parallel, resulting in lower strength but high heat resistance. - Does not cover inorganic high-strength fibers such as carbon fiber or glass fiber. ## The clever bit Instead of trying to melt the polymer, Kwolek dissolved the rigid, stubborn polymer into a liquid-crystalline solution. This allowed the molecules to pre-align perfectly parallel to each other before being extruded through the spinneret, achieving unprecedented strength without needing extreme post-stretching. ## Real-world examples 1. Kevlar bulletproof vests 2. High-performance radial car tires 3. Mooring lines for offshore oil rigs 4. Fiber-optic cable reinforcement 5. Aerospace composite panels ## Why it matters This patent laid the foundation for Kevlar, one of the most important materials of the 20th century. It enabled lightweight body armor (bulletproof vests) that saved thousands of lives, as well as high-performance radial tires, aerospace composites, and deep-sea cables. ## Frequently asked questions ### What does The Molecular Structure of Kevlar High-Strength Fiber cover? 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. ### Who owns patent US 3819587? EI Du Pont de Nemours and Co owns this patent, granted in 1974. ### 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 3819587 cited by? This patent has been cited by 141 later patents that build on its ideas. ### What problem does this patent solve? This patent laid the foundation for Kevlar, one of the most important materials of the 20th century. It enabled lightweight body armor (bulletproof vests) that saved thousands of lives, as well as high-performance radial tires, aerospace composites, and deep-sea cables. ### What does this patent NOT cover? Does not cover aliphatic polyamides like nylon, where the carbon chains are flexible and do not contain rigid aromatic rings. **Full plain-English explainer:** https://patentbrief.org/patent/us/3819587/kevlar-aramid-fiber-kwolek **Original patent:** https://patents.google.com/patent/US3819587 --- _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 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. - [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 Spandex Elastic Fibers Are Chemically Engineered](https://patentbrief.org/patent/us/2929804/spandex-lycra-elastic-fiber) — DuPont's 1960 patent for a stretchy, durable synthetic fiber made from segmented polymers, which became the foundation for modern Spandex. - [How Plastic Soda Bottles Are Made Stronger Using Stretched Molecules](https://patentbrief.org/patent/us/3733309/pet-plastic-bottle) — A 1970s invention that describes how to make lightweight, clear plastic bottles strong enough to hold carbonated drinks without exploding. - [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.