What Is Elastane? Spandex vs Elastane vs Lycra, and What It's Made Of

In 1966, a group of English doctors wrote to the BMJ about 11 women with the same rash. It showed up wherever their bras touched their backs and the front of their chests, everywhere except under the cups. All 11 had been wearing one brand of bra. Patch tests traced the reaction to mercaptobenzothiazole, a rubber chemical that had been used in making that bra's spandex. A Lycra yarn the doctors tested at the same time came back negative (BMJ, 1966).

We bring it up because it's still the most useful way to think about the "5% elastane" on your leggings or jeans. There's the stretch fiber itself, and there's whatever went into making it. Below is what elastane actually is, why spandex and elastane are the same thing, and what's known (and not known) about wearing it.

What is elastane?

Elastane is a synthetic stretch fiber. In the US its legal name is spandex, and the Federal Trade Commission's textile rule defines spandex as "a manufactured fiber in which the fiber-forming substance is a long chain synthetic polymer comprised of at least 85 percent of a segmented polyurethane" (16 CFR 303.7).

"Segmented" is the important word. The Museum of Design in Plastics describes elastane as polyurethane organized in rigid and flexible segments, which is what gives it its stretch and recovery. The more elastane in a garment, the museum notes, the closer and firmer the fit.

A little goes a long way. Lycra's own history page says the original fiber could stretch up to 500% of its length and return to shape over and over. Textile researchers writing in Biomacromolecules in 2024 note that 2 to 5 percent elastane is enough to improve the function and comfort of a cotton fabric.

Elastane vs spandex: is there a difference?

No. They're two names for the same fiber.

Spandex is the American generic name. Elastane is the name used in ISO 2076, the international standard for man-made fiber names, and the FTC's rule incorporates that standard. The FTC's labeling guide for businesses says the ISO standard uses "elastane for spandex. You may use either name." The National Inventors Hall of Fame puts it simply: Lycra "is known as elastane in Europe and throughout most of the world."

So if one pair of leggings says spandex and another says elastane, you're looking at the same material.

What is Lycra?

Lycra is a brand of spandex. DuPont chemist Joseph Shivers developed it in the 1950s while trying to find a synthetic replacement for the heavy rubber threads used in foundation garments, according to the National Inventors Hall of Fame. Lycra dates his "Fiber K" to 1958.

Because Lycra is a trademark, US rules don't let it stand in for the fiber name. The FTC's labeling guide says a fiber trademark has to appear next to the generic name, with this example:

80% Cotton 20% Lycra® Spandex

What is spandex made of?

It starts from fossil fuels. The Museum of Design in Plastics lists petroleum and natural gas as its common starting materials.

A 2000 EPA economic analysis of spandex production lays out the usual process. A diisocyanate (commonly MDI or TDI) is reacted with a polyol to make a prepolymer. That gets dissolved in a solvent and reacted with a diamine to build the long polymer chain. Then it's spun. The EPA says 80 to 90 percent of the world's spandex is dry spun: the solution is pushed through tiny holes into a heated tower, where the solvent evaporates and leaves solid fibers behind. A US patent on spandex manufacturing names dimethylacetamide (DMAc) as the preferred solvent, with dimethylformamide (DMF) and DMSO as other options.

Two details from the EPA documents are worth knowing if you care about what's left in the fiber. The economic analysis says freshly spun fibers "may still contain some solvent which may have to be removed through washing or further heating," and that chemical finishes are added after spinning. The EPA's older emissions guide for synthetic fibers, from the 1990s, says the residual solvent in spandex leaving the spinning cell is considerably lower than in other dry spun fibers. Neither document says how much, if any, reaches the finished garment you buy.

Is spandex plastic?

Yes. Polyurethane is a synthetic polymer, which puts spandex in the same family as polyester and nylon. (We looked at nylon the same way in Is Nylon Plastic?) Our elastane material guide shows how we score the fiber on its own.

That also means elastane is part of the microplastics question. We haven't found good data on how much elastane sheds compared with polyester, so we're not going to guess. Our post on microplastics from clothing covers what's known about synthetic fabrics in general.

Is elastane bad for you?

The skin reports we found come from the 1960s, and they point at a processing chemical, not at spandex as a whole. Doctors at the Hitchcock Clinic in Hanover, New Hampshire, reported allergic dermatitis matching the spandex parts of bras, with every patient also reacting to mercaptobenzothiazole (Archives of Dermatology, 1967). A University of California, San Francisco report the same year found that most of its spandex-sensitive patients' reactions "presumably" related to trace mercaptobenzothiazole in "certain but not all brands," and those patients could wear brands that appeared free of it (JAMA, 1967).

What we couldn't find is recent research that measures what, if anything, moves from today's elastane into skin during normal wear. So we can't tell you it's harmless, and we can't tell you it's a problem. If you get a rash that lines up exactly with waistbands or stretch panels, that's the pattern those doctors described, and a dermatologist can patch test for it.

If you're weighing something like 90% modal and 10% spandex underwear, the main fiber is still most of the fabric, so it's worth looking at that fiber and how the garment was finished, not only the stretch percentage. Our guide to the healthiest fabrics to wear goes fiber by fiber.

Why elastane makes clothes hard to recycle

Elastane gets in the way whether old clothes are shredded or dissolved. A 2025 study in the journal Analyst says elastane fibers "can hamper mechanical and chemical fiber recycling," and the Biomacromolecules researchers write that even small amounts in a cotton blend "can prevent fiber-to-fiber recycling," the kind that dissolves old cotton and spins it into new fiber.

It's also hard to spot. In Fashion for Good's Sorting for Circularity Europe project, which sorted used clothes with handheld near-infrared scanners, the sorters' handbook says elastane "is hardly recognised by the scanner." The Biomacromolecules team did show they can strip elastane out of cotton blends in the lab, getting it below 0.08%, but that's a lab method, not something your local textile bin does.

Does elastane wear out?

It can, and how you wash it matters, so if you're wondering whether a pair of 99% cotton, 1% elastane jeans will last, the wash is a big part of the answer. Toray Lycra, a Japanese company that makes Lycra fiber, publishes care advice for Lycra garments (the page is in Japanese). In short:

• Wash at 40°C (104°F) or below. Toray says hotter water can make dyes run.
• Use a mesh bag in the machine so the garment doesn't twist out of shape.
• Use oxygen bleach if you need bleach. Toray says to absolutely avoid chlorine bleach because it degrades the fiber.
• Rinse well. Toray says leftover detergent can contribute to degradation.
• Dry in the shade, out of direct sun.
• Iron at medium heat with a pressing cloth. Toray says an iron touching the Lycra fiber directly can cause spots of shrinking and distortion.

How to spot elastane on a clothing tag

Spandex, elastane and "Lycra® spandex" all mean the same fiber family. A few other label rules are worth knowing:

• Small amounts can show up as "other fiber." Under 16 CFR 303.3, a fiber under 5% is normally listed as "other fiber" unless it has a clear functional purpose. The FTC's own example of a fiber worth naming anyway is "4 percent Spandex," since stretch is the whole point.
• Waistbands may not count. Under 16 CFR 303.12, waistbands, cuffs and elastic added for structure are treated as trim, and elastic that's part of the fabric can be left out of the fiber line if it covers no more than 20% of the garment's surface area, as long as the label says "exclusive of elastic." That's how a pair of joggers with a stretchy waistband can still say 100% cotton. We explained the trim rules in more detail in what "exclusive of trim" means.

When you shop with Greener Closet, spandex shows up in a product's breakdown when the brand lists it. We only score what the listing discloses, so if a brand leaves the stretch fiber off, we can't add it.