The fiber-content label is the only reliable proof: a sweater is truly 100% cotton only when its sewn-in label says so, because U.S. law requires the actual fiber percentages to be disclosed.
A soft, matte knit feels like cotton, but feel proves nothing — a cotton-poly blend can fool your fingertips for years. The answer lives on a small tag inside the side seam, and it is legally required to tell the truth. Under the FTC’s textile labeling rules, a sweater can only carry the words “100% Cotton” when cotton is the only fiber in the main body of the garment, aside from limited trim.
Here is what to look for, what the label legally must say, and which “tests” are a waste of time.
What Does the Fiber-Content Label Legally Have to Say?
Every covered sweater sold in the U.S. must carry a label listing fiber content, country of origin, and the manufacturer or marketer’s identity.
The FTC requires generic fiber names and their percentages by weight, listed in descending order of predominance. So a blend tag reads “60% Cotton, 40% Polyester” — the largest fiber first. That order is a fast tell: if anything other than cotton leads, the sweater is not 100% cotton. The FTC also requires the label to disclose each fiber’s percentage by weight, excluding limited ornamentation.
Reading the Label the Right Way
Look for the exact string “100% Cotton” (or “100% Pima Cotton”), because the FTC only allows those claims when the fiber content backs them up.
The FTC’s “Calling It Cotton” guidance is specific about the Pima case: a garment may be labeled “100% Pima Cotton” only if it contains 100% Pima cotton fibers — no blending down with ordinary cotton while keeping the premium name.
Then scan for the fibers that break the claim:
- Polyester, nylon, acrylic, or rayon — any of these means it is a blend, not pure cotton.
- Elastane or spandex — added for stretch; even 2% disqualifies a “100% cotton” claim.
- Wool — a mixed-fiber knit cannot be labeled 100% cotton.
The FTC’s rules also allow non-cotton trim on a product still labeled “100% Cotton,” so a decorative neckline thread or a small woven tag doesn’t automatically void the claim. The catch is that the label describes the main textile fiber content, not every incidental component. If a seller’s description says “100% cotton” but the sewn-in tag lists a blend, trust the tag.
That tolerance comes from secondary interpretation, not the FTC’s own consumer pages, so treat it as background, not a green light to accept a visible “95% Cotton” tag.
Why Feel Tests and Burn Tests Fall Short
Touching a sweater cannot verify fiber content, and burning threads off a garment is dangerous and can ruin it.
Cotton does feel soft and matte, and it wrinkles rather than snapping back. Those traits are suggestive, not proof — plenty of blends are engineered to feel identical. The FTC’s consumer guidance does not endorse feel as a verification method, and it does not recommend burn testing at all. Burning fabric is a fire hazard, the results are hard to read without training, and testing a finished sweater damages it. Skip both methods.
Instead, use the tag. If you’re replacing a sweater that failed the label check, our tested roundup of 100% cotton crewneck sweaters lists options that pass it.
Where Care and Fiber Labels Sit on a Sweater
Fiber content and care instructions are usually on separate tags, and both should be easy to find before you buy.
The FTC’s care-label guidance says clothing labels should be attached so consumers can see or find them at the point of sale — meaning a sweater that hides its fiber tag isn’t doing you a favor. On most sweaters, the fiber tag sits in the left side seam; the care tag often sits nearby or at the back neckline.
| Label Reads | What It Means | Verdict |
|---|---|---|
| 100% Cotton | Only cotton in the main body, aside from permissible trim | Pure cotton |
| 100% Pima Cotton | Must contain 100% Pima cotton fibers, per the FTC | Pure Pima cotton |
| 95% Cotton, 5% Elastane | Blend with added stretch | Not 100% cotton |
| 60% Cotton, 40% Polyester | Cotton is majority, but blended | Not 100% cotton |
| 70% Cotton, 30% Recycled Polyester | Blended with synthetic fiber | Not 100% cotton |
| 100% Cotton (trim: 100% Polyester) | Cotton body with non-cotton trim | Pure cotton main body |
| No fiber tag at all | Required disclosure missing | Cannot be verified |
The FTC’s labeling requirements live in its cotton labeling and advertising guidance, which spells out when the “100% Cotton” claim is allowed.
Two limits worth remembering. These rules are U.S.-specific — a sweater bought from an overseas seller may follow different disclosure laws. And a sweater can legally carry non-cotton trim while still reading “100% Cotton,” so the claim covers the main knit, not every thread and finish. Neither caveat changes the core rule: the sewn-in fiber label is the one piece of evidence a sweater cannot fake.
FAQs
Is a 95% cotton sweater close enough to pure cotton?
No, not on paper. The FTC’s labeling framework ties the “100% Cotton” claim to the fiber content itself, so a tag reading 95% cotton with 5% elastane is a blend, full stop. The 5% adds stretch and changes how the knit wears and washes, so judge it as its own material, not as pure cotton.
Can a sweater be labeled 100% cotton if the trim is polyester?
Yes. The FTC permits limited non-cotton trim on a product still labeled “100% Cotton,” because the claim addresses the main textile fiber content rather than every decorative component. A polyester neckline thread or woven brand tag does not void the claim on its own. Check the main body fiber listing for the real answer.
Does “100% organic cotton” mean the same thing as “100% cotton”?
Not quite. “Organic” speaks to how the cotton was grown and certified, while the percentage speaks to fiber content. A sweater can be 100% cotton without being organic, and an organic claim is verified through separate certification programs. Read the fiber percentage and the organic certification as two different pieces of information.
References & Sources
- Federal Trade Commission. “Calling It Cotton: Labeling and Advertising Cotton Products.” Sets the rules for when a product may claim “100% Cotton” or “100% Pima Cotton.”
- Federal Trade Commission. “Threading Your Way Through the Labeling Requirements Under the Textile and Wool Acts.” Explains required fiber content, country of origin, and manufacturer disclosure on textile labels.
- Federal Trade Commission. “Clothing and Textiles.” Overview of FTC labeling and care rules for apparel sold in the U.S.