What is nylon fabric? The federal definition, the label rules and the 1940 stocking launch

Nylon is a manufactured fiber, and federal rules define it narrowly. Under 16 CFR 303.7(i), nylon is "a manufactured fiber in which the fiber-forming substance is a long-chain synthetic polyamide in which less than 85 percent of the amide linkages are attached directly to two aromatic rings." In plain terms, it is a plastic spun into thread, strong and light, and it became a household word in 1940 when DuPont put stockings made from it in American stores. The rest of this piece covers what the label must say and the sales story, with the sources' disagreements flagged.

The federal definition

We read paragraph (i) on the Electronic Code of Federal Regulations as it stood on October 20, 2026. The definition sets a boundary. A polyamide where 85 percent or more of the amide linkages attach directly to two aromatic rings falls under a different generic name, aramid. Everything below that line, which includes the nylon in jackets, tights and backpacks, is nylon on a label.

The Textile Fiber Products Identification Act rules require a label to name each fiber by its generic name and percent by weight. A product that is 100 percent nylon says so. A blend lists each fiber present at 5 percent or more, and our explainer on fiber content label rules covers the exceptions. Polyester is the other big synthetic, with its own definition in the same section; see what polyester is.

The stocking story, and why the dates differ

Smithsonian Magazine's May 11, 2015 article by Kimbra Cutlip says nylon stockings made their debut at the 1939 World's Fair in New York, went on sale to the public on May 15, 1940, and that four million pairs sold out in four days. It quotes Susannah Handley: "Nylon became a household word in less than a year."

A 2012 Smithsonian Magazine piece by Emily Spivack gives a slightly different account. It says the first 4,000 pairs sold out in about three hours at DuPont's Wilmington experimental station in 1939. Its date for "Nylon Day" is May 16, 1940, when roughly four million pairs reached stores at about $1.15 a pair and sold out within two days.

So two articles from the same magazine disagree on the day (May 15 or 16) and on how fast the pairs sold (four days or two). We do not know which is right, and we did not find a DuPont or museum record that settles it. The safe version: the stockings went on sale in mid-May 1940, about four million pairs were involved, and they sold out within days.

What war did to nylon

Spivack's piece says that after Pearl Harbor, nylon was severely rationed and redirected to the war effort. It was not fully halted, but its permitted uses included parachutes, tire cords and ropes. Cutlip's piece says nylon was diverted to parachutes, which had previously been made of silk.

When rations eased, the demand showed. Spivack reports that in autumn 1945, crowds lined up across the country, and in Pittsburgh about 40,000 people queued for roughly a mile for 13,000 pairs. Those figures are the article's, and it places the so-called nylon riots in 1945.

What nylon is good and bad at, as sources show

The sources we opened support a narrow list of claims. The 2015 article ties nylon to parachutes, which implies strength and light weight, but it does not publish a strength test. The federal definition says nothing about performance at all. It is a chemistry boundary, not a quality grade. Claims about durability, quick drying or pilling resistance come from vendors, and we did not open independent testing for this piece, so we do not rate them.

Labels and claims to watch

Three habits help when you shop. Check that the percent of nylon on the sewn label matches the product page. Watch for words that imply a fiber that is not there: section 303.18 bars words that imply a fiber that is absent or sound like one. And treat "recycled nylon" or "eco nylon" as a claim that needs a named certification or a measured percent, not a description of the polymer. The federal definition does not distinguish between virgin and recycled nylon.

Why a 1940 sales story still matters

The stocking episode is the usual origin story for synthetics in fashion. It shows a manufactured fiber replacing silk in a mass market, then a war pulling it away, then a shopping frenzy when it returned. It also shows how much of fashion history rests on repeated numbers. Four million pairs appears in both Smithsonian pieces, which is why we give it, but the timing is where they split.

A note on the sources

Both Smithsonian Magazine articles are independent of DuPont, but both are popular histories, not company records. We read neither the original DuPont sales ledgers nor a museum catalog entry, so every sales figure here is reported, not audited.

Our take

Read nylon as a defined, regulated fiber name and a well documented piece of fashion history, not as a quality promise. Check the label percent, discount vague eco words, and when you read about the 1940 launch, remember that even careful sources disagree on the date by a day and on the sell out by two days. That kind of gap is why we show our sources, and why a tidy number deserves a second look. If you need to cite the launch, say mid-May 1940 and name the article you took it from.