How to Tell if Sheets Are Really 100% Cotton

You’d think “100% cotton” would be the end of the conversation. It’s printed right there on the package. But a sheet set can carry that label legally while being sewn with polyester thread, finished with a polyester-blend elastic band, and sold under a name that sounds like it’s made of something else entirely.

That isn’t usually fraud. It’s how US labeling rules work. The rules decide which parts of a product have to be counted, and which parts the label is allowed to leave out. Once you know where the gaps are, checking a sheet set takes about two minutes.

Step 1: Find the real label, not the packaging

In the US, sheets are covered by the Textile Fiber Products Identification Act, which the Federal Trade Commission (FTC) enforces. Covered products need a label that lists every fiber by its generic name (cotton, polyester, rayon and so on) and its percentage by weight, in order from most to least.¹

A few details in those rules are useful to shoppers:

• “All cotton” means the same as “100% cotton.” The FTC lets a single-fiber product use either wording.¹
• There’s no wiggle room on “100%.” Blended products get a 3% manufacturing tolerance (a “40% cotton” label can really be 37% to 43%). That tolerance doesn’t apply when a label says a product is made of one fiber. The FTC’s own example: a blouse that’s 97% silk and 3% polyester can’t be labeled “100% silk.”¹
• Small amounts can hide as “other fiber.” Fibers under 5% of the weight are usually listed as “other fiber” or “other fibers,” not by name. So “95% cotton, 5% other fiber” isn’t a 100% cotton product, even if it sounds close.¹
• Stretch fibers can be named even in small amounts. If something like spandex is added for a functional reason, the label can name it even at under 5%, as in “96% cotton, 4% spandex.”²

The FTC also says plainly that a product shouldn’t be labeled “100% cotton” unless it contains only cotton, “or only cotton with some non-cotton ‘trim’.”² That last phrase is where most of the surprises live.

Step 2: Check what the label is allowed to leave out

US rules exempt several parts of a textile product from the fiber statement. For sheets and bedding, three of them matter most.

Sewing thread

The Textile Act exempts “sewing and handicraft threads,” and the FTC’s rules treat threads used “in minor proportion for holding, reinforcing or similar structural purposes” as trim.³⁴ In plain terms, the thread that holds the hems and seams together doesn’t have to appear on the label.

That matters because cotton thread is no longer the default. Coats, one of the world’s largest thread makers, says that “most sewing threads today are based on synthetic materials, such as polyester or nylon.” It calls polyester-core thread wrapped in cotton, known as corespun, “the best general-purpose apparel sewing thread available in the market today.”⁵ So a sheet set with a perfectly honest “100% cotton” label may well be stitched with polyester. The only way to know is to ask.

Elastic (the big one for fitted sheets)

Most fitted sheets hold on to the mattress with an elastic band around the edge. Under the FTC’s rules, elastic added in minor proportion for structural purposes counts as a “finding” (a type of trim) and doesn’t need to be disclosed. Elastic that’s part of the basic fabric can also be left out if it covers no more than 20% of the product’s surface area, as long as the label adds the words “exclusive of elastic.”⁴¹

So when you see “100% cotton, exclusive of elastic,” read it literally: the cotton figure doesn’t include the elastic, and the label doesn’t have to tell you what the elastic is made of.

Decoration, piping and embroidery

Decorative trim, such as embroidery, piping or an applique, is exempt if it covers no more than 15% of the surface area. In that case the label should say “exclusive of decoration.”⁴¹ A pillowcase with a contrast-stitched border or a duvet cover with embroidered edging can be “100% cotton exclusive of decoration” even if the decoration is polyester or rayon.

Buttons, zippers and other hardware

Fiber labels only cover fibers. Non-fibrous parts like buttons, snaps, zippers and beads don’t have to be listed.¹ That’s mostly a duvet cover and pillow sham question. Plastic buttons don’t make the fabric any less cotton, but if you’re trying to avoid plastic altogether, they’re worth asking about. (On our picks, natural coconut-shell and nut buttons are allowed, and every product card names the closures.)

Step 3: Decode the marketing words

Product titles and packaging fronts aren’t held to the same format as the fiber label. Some words that cause confusion:

• Sateen, percale, poplin, flannel, jersey. These are weaves or knits, not fibers. You can buy polyester sateen and polyester flannel. “Cotton sateen” tells you the fiber; “sateen” alone doesn’t.
• “Cotton-rich,” “cotton blend,” “cotton feel,” “cotton touch.” None of these are fiber percentages. If the label lists anything besides cotton, it isn’t 100% cotton, however it feels.
• Egyptian, Pima, Supima, Sea Island. These are types of cotton. The FTC lets a label name them only if it’s truthful. A sheet that’s 65% Pima and 35% Upland cotton can say “100% cotton (65% Pima cotton),” but it can’t be called “100% Pima cotton.”² Good news for our purposes: any honest label naming only cotton types is still 100% cotton.
• “Bamboo.” Most soft “bamboo” sheets are rayon (viscose) made from bamboo pulp. In 2022 the FTC sought $5.5 million in penalties from Kohl’s and Walmart for marketing rayon textiles as bamboo.⁶ Bamboo-cotton blends aren’t 100% cotton.
• Microfiber. Microfiber is a fine synthetic fiber, usually polyester. It isn’t cotton.

Shopping online? The FTC’s rules apply to internet ads too. If a listing mentions a fiber, it’s supposed to name all the fibers in order of predominance, though it doesn’t have to give percentages.¹ If a listing says “soft cotton feel” and never gives a full fiber list, treat that as a reason to look harder.

Step 4: Don’t let thread count do the talking

Thread count is the number of threads in a square inch of fabric, counted in both directions. It says nothing about fiber content, and it’s often inflated.

Some sellers used to multiply the count by the number of plies twisted into each thread, turning a 300-thread-count sheet into a “600” or even “1,000.” In 2005 the FTC’s staff said that practice could mislead consumers. They pointed to the ASTM test method, which counts each yarn as one, plied or not, and suggested disclosures like “300 thread count, 2-ply yarn” instead of “600 thread count.”⁷

For a purity check, thread count just isn’t relevant. A 1,000-count sheet can be a cotton-polyester blend, and a 200-count percale can be 100% cotton in every part.

Step 5: Check certifications properly

Certifications are useful, but each one answers a different question, and none of them is a guarantee of “100% cotton everything.”

• GOTS (Global Organic Textile Standard) has two label grades. “Organic” needs at least 95% certified organic fibers, and “made with organic materials” needs at least 70%. Both percentages are calculated excluding accessories, and GOTS’s accessory list includes sewing threads and elastic bands.⁸ A GOTS logo tells you a lot about how the product was made, but you still need to read the fiber label.
• OEKO-TEX STANDARD 100 is a test for harmful substances, not a fiber or organic claim. Its tests cover “every thread, button and accessory,” which is reassuring, but a polyester sheet can carry the label too.⁹
• OCS (Organic Content Standard) tracks organic material through the supply chain. It “does not address the use of chemicals or any social or environmental aspects of production.”¹⁰

We go through what each one covers, and how to verify them, in GOTS vs OEKO-TEX vs OCS: What Cotton Certifications Actually Mean.

Always look the number up. GOTS goods should carry the license number of the certified company, which you can search in the GOTS public database.⁸¹¹ OEKO-TEX labels have a number you can enter in the OEKO-TEX Label Check.¹² If the number doesn’t come up, or belongs to a different kind of product, don’t rely on the logo.

Step 6: Test at home (and know the limits)

If you already own the sheets and the label is gone, there are a couple of home checks. Neither one is proof.

The feel-and-wrinkle check. Many people notice that all-cotton woven sheets crease more readily out of the dryer than polyester blends do. Treat that as a hint at most: weaves and “wrinkle-resistant” finishes change how fabric behaves, so it proves nothing.

The burn test. Textile conservators and educators use small burn tests to tell plant fibers from synthetics. Cotton catches fire readily, keeps glowing after you take the flame away, smells like burning paper and leaves soft, light gray ash. Polyester tends to melt and leaves a hard, dark bead.¹³¹⁴

If you try it:

1. Snip a few threads from a seam allowance or hem. Never hold a flame to the sheet itself.
2. Hold the threads with metal tweezers over a sink, a metal tray or a glass dish, away from anything flammable, with a window open.
3. Let them burn out, then check the residue after it cools. Ash that crumbles to powder suggests a plant fiber. A hard bead you can’t crush suggests a synthetic.

The big limitation: rayon, viscose, lyocell, bamboo viscose and linen all burn much like cotton. These fibers are all made of cellulose, which is why they burn with the same papery smell.¹⁴¹³ A burn test can catch hidden polyester, but it can’t tell cotton from bamboo rayon. Blends can also give mixed results. Fabric coatings can throw it off as well, because the coating burns first.

If you really need to know, textile labs use standard methods like AATCC TM20 to identify fibers and TM20A to measure the percentages in a blend.¹⁵ That’s overkill for a single sheet set. It’s how brands and importers check their suppliers, though.

Step 7: Ask the brand (and what to ask)

For the parts a label doesn’t cover, the brand is the only real source. A good brand will answer quickly. This is the message we send, and you’re welcome to copy it:

Hi, before I buy the [product name], could you confirm the fiber content of each part?

1. Main fabric
2. Sewing thread
3. Elastic, if any (and whether it contains spandex, polyester, nylon or rubber)
4. Labels, piping or other trims
5. Buttons or closures

Thank you!

If the answer is vague (“premium materials”), or only repeats the front of the package, treat the unconfirmed parts as not cotton.

Why bother: labels can be wrong

Even a correct-looking label depends on the supply chain behind it. In 2016, Target said its investigation found that a supplier had substituted non-Egyptian cotton in Fieldcrest-brand sheets and pillowcases sold as Egyptian cotton. Target pulled the products, offered refunds and ended the relationship.¹⁶ That case was about the type of cotton, not cotton versus polyester, but the lesson carries over. Buy from brands that publish detailed specs, keep the receipt, and favor certifications you can look up.

What a sheet has to pass before we list it

When we recommend sheets on Must Be Cotton, every one has to clear the same bar:

• The fiber label says 100% (or all) cotton, with no “exclusive of elastic” or “exclusive of decoration” caveats we haven’t resolved.
• The sewing thread is confirmed cotton, not polyester and not polyester-core (corespun) thread.
• There’s no elastic, or the brand confirms the elastic is entirely cotton. In practice, that means flat sheets and tie or drawstring fitted styles.
• Labels and trims are cotton. Any buttons or closures are named on the product card; natural coconut-shell and nut buttons are allowed.
• Any certification is verified in the issuer’s database.

Products that can’t clear all five don’t make the list, however good they are otherwise.

Frequently asked questions

Can sheets labeled 100% cotton contain polyester?

Yes, in the parts the label is allowed to skip. US rules exempt sewing thread, small trims and, in some cases, elastic from the fiber content statement, so a legal "100% cotton" label can sit on a sheet sewn with polyester thread or finished with synthetic elastic. The main fabric itself must be all cotton; the 3% tolerance for blends does not apply to single-fiber claims.

What does "exclusive of elastic" mean on a fitted sheet?

It means the fiber percentage on the label does not include the elastic. Under FTC rules, elastic covering no more than 20% of the surface area can be left out of the fiber statement as long as the label says "exclusive of elastic." The label does not have to say what the elastic is made of, so you need to ask the brand.

Is cotton sateen always 100% cotton?

No. Sateen is a weave, not a fiber, and it can be made from cotton, polyester or blends. Check the fiber label for "100% cotton" or "All cotton."

Does a burn test prove sheets are 100% cotton?

No. A burn test can suggest whether a sample contains a melting synthetic like polyester, but rayon, viscose, lyocell, bamboo viscose and linen burn much like cotton, and blends give mixed results. Only lab methods such as AATCC TM20 and TM20A identify and measure fibers reliably.

Does an OEKO-TEX label mean sheets are organic or 100% cotton?

No. OEKO-TEX STANDARD 100 means the product was tested for harmful substances. It is not a fiber content or organic claim, and synthetic products can be certified. OEKO-TEX runs a separate ORGANIC COTTON certification.

Are there fitted sheets without elastic?

Flat sheets have no elastic at all. Fitted-style designs that use cotton ties or a cotton drawstring instead of an elastic band would also meet our all-cotton rule, as would elastic a brand confirms is entirely cotton. We only list a fitted option after the brand confirms every part.

Sources

Footnotes

1. Federal Trade Commission, Threading Your Way Through the Labeling Requirements Under the Textile and Wool Acts. Covers fiber names and percentages, “All” vs “100%,” the 5% “other fiber” rule, trims, elastic, decoration, non-fibrous parts, tolerances and advertising. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸

2. Federal Trade Commission, Calling It Cotton: Labeling and Advertising Cotton Products (July 2014). ↩ ↩² ↩³

3. Federal Trade Commission, Textile Fiber Products Identification Act, 15 U.S.C. § 70j (exemptions). ↩

4. 16 CFR § 303.12, Trimmings of household textile articles (eCFR). ↩ ↩² ↩³

5. Coats Group, Thread Production (technical bulletin). ↩

6. Federal Trade Commission, FTC Uses Penalty Offense Authority to Seek Largest-Ever Civil Penalty for Bogus Bamboo Marketing from Kohl’s and Walmart (April 8, 2022). ↩

7. FTC staff opinion letter to the National Textile Association on thread count, August 2, 2005 (PDF), citing ASTM D3775. ↩

8. Global Standard gGmbH, Global Organic Textile Standard (GOTS) Version 8.0 (released March 2, 2026), sections 2.7.5–2.7.6 and 3.3.2. ↩ ↩²

9. OEKO-TEX, OEKO-TEX STANDARD 100. ↩

10. Textile Exchange, What is the Organic Content Standard (OCS)? ↩

11. GOTS, Certified Suppliers database. ↩

12. OEKO-TEX, Label Check. ↩

13. Canadian Conservation Institute, The Identification of Natural Fibres (CCI Notes 13/18). ↩ ↩²

14. Museum of Fine Arts, Boston, CAMEO, Fiber burn test. ↩ ↩²

15. AATCC, TM20A, Test Method for Fiber Analysis: Quantitative; TM20 covers qualitative fiber identification. ↩

16. Target, Target Statement on Welspun Global Brands (August 2016). ↩

Facts in this article were last checked on October 20, 2026. Spotted something out of date? Tell us; we correct errors and note the change.

Get the pure-cotton list

New verified 100% cotton finds and the latest research, about twice a month. No spam.

Email addressSign up

Leave this field empty

I agree to receive the Must Be Cotton newsletter by email. We store your email address on Cloudflare and use it only for this newsletter. We never sell it. Unsubscribe any time by replying to [email protected]. See our privacy policy.