Is Silk Natural or Synthetic? What Silk Is Made Of
Is silk natural or synthetic? Silk is a natural fibre, not a synthetic one: it is a protein fibre (built from proteins) that silk-producing insects, above all the silkworm, spin to make their cocoons. The question comes up because the word silk, and words that sound like it, also appear on fabrics made of polyester, viscose or acetate. This guide sorts the fibres and the names apart.
What silk is made of
Silk is made of two main proteins: fibroin, which forms the filaments, and sericin, a gum that surrounds the fibroin filaments and holds them together. The best-known silkworm, Bombyx mori, is a moth larva, and its cocoon protects it while it becomes a moth.
According to a 2016 review on Bombyx mori sericin, one cocoon is formed by one long silk thread of 900 to 1,500 metres; fibroin and sericin make up 98% of its structure, and sericin alone accounts for 25 to 30% of the cocoon's weight.
Before silk is used for textiles, most of the sericin is removed by degumming, the stripping of this gum with hot water and mild chemical treatments, as a 2022 study describes it. The remaining fibroin is made into silk yarns and fabrics. How silk is made, from the cocoon to the woven fabric, is covered in our guide to what silk is.
Natural, synthetic, or made from a natural raw material
“Natural or synthetic” leaves out a third group of fibres. Natural fibres such as wool, silk, cotton and linen come from animals or plants, and the University of Georgia Extension classes both silk and wool as natural protein fibres. Synthetic fibres such as polyester are spun from polymers made by chemical synthesis.
Viscose and acetate belong to the third group: they are manufactured fibres, but their raw material is cellulose from plant sources such as wood and cotton. Viscose is a regenerated cellulose fibre, meaning cellulose that is dissolved and then solidified back into filaments, and acetate is cellulose acetate, a derivative of cellulose. A plant raw material does not make viscose a natural fibre, and raising silkworms and degumming their cocoons do not make silk a manufactured one: the EU regulation on textile fibre names lists silk in the first table of its Annex I with wool, cotton and flax (linen), and acetate, viscose and polyester in a second table. Our guide to artificial silk explains how viscose and acetate differ from silk.
| Fibre | Raw material | Category | Legal definition in short |
|---|---|---|---|
| Silk | Cocoons of silk-producing insects, above all the silkworm | Natural protein fibre | EU: fibre obtained exclusively from silk-secreting insects (Annex I No 4) |
| Polyester | Synthetic polymer | Synthetic fibre | EU: fibre made mainly of an ester of a diol and terephthalic acid (Annex I No 35); US: long-chain synthetic polymer (16 CFR 303.7(c)) |
| Viscose | Cellulose | Manufactured from a natural raw material | EU: regenerated cellulose fibre obtained by the viscose process (Annex I No 25); rayon in the US rules (16 CFR 303.7(d)) |
| Acetate | Cellulose | Manufactured from a natural raw material | EU: cellulose acetate fibre (Annex I No 19); US: cellulose acetate (16 CFR 303.7(e)) |
Why so many fabrics borrow the name
Early fibres made from cellulose were sold as artificial silk. A historical Kansas State College bulletin records that these fibres went under that name because they resembled silk, and that Count Hilaire de Chardonnet produced the first commercial artificial silk from nitrocellulose. The bulletin adds that the United States later adopted the name rayon for the yarns known as artificial silk.
Silk is a natural fibre, while satin is a weave that is often made of polyester or another synthetic fibre. Silk woven in a satin weave is called silk satin, and that is the one place where the two words genuinely meet. Our guide to silk vs satin compares the two.
Words like “silky”, “satin finish” or “silk-touch” are not fibre statements. Such words describe a look or a feel, while the fibre composition on the label names the material.
What the law says about the word silk
In the EU, Regulation (EU) No 1007/2011 on textile fibre names defines silk in entry 4 of its Annex I as “fibre obtained exclusively from silk-secreting insects”. Article 5(2) reserves each listed name for fibres that match its description and states that the names “shall not be used for other fibres, whether on their own or as a root or as an adjective”. It also bars the term silk from describing the shape or presentation of textile fibres in continuous filament yarn.
Under these rules, polyester may not be called silk in the fibre composition on an EU label or marking. Under Article 16(1), that composition has to be clearly visible to the consumer before the purchase, including online. The UK applies its retained version of the regulation, worded the same in Article 5 and the Annex I silk entry.
In the United States, 16 CFR Part 303, the rules under the Textile Fiber Products Identification Act, has no definition of silk: the word appears only in examples, such as the list of generic fibre names in section 303.6. Section 303.7 defines manufactured fibres such as polyester, rayon and acetate. Section 303.18 states that words, coined words, symbols or depictions that name or imply a fibre which is not present, sound like its name, or vary its spelling only slightly “shall not be used in such a manner as to represent or imply that such fiber is present in the product”. This section is a summary, not legal advice.
How to tell whether silk is real
To tell whether silk is real, look first at the fibre composition on the label or product page. Article 7(1) of the EU regulation reserves “100%”, “pure” and “all” for products composed exclusively of one fibre, so “100% silk” declares silk to be the fibre; Article 7(2) allows up to 2% by weight (5% after carding) of technically unavoidable other fibres.
The burn test is often suggested, but it is not conclusive. Textile conservators of the American Institute for Conservation describe burning as a way to learn a fibre's family, such as protein, cellulose or synthetic fibres, and note that it cannot identify blends and that some finishes affect the result. Silk is not the only protein fibre: wool is one too. Only a laboratory fibre analysis settles for certain whether a fabric is silk. Our guide to artificial silk and real silk covers the other clues and their limits.
Natural does not mean better for everything
Natural tells you what a fibre is and where it comes from, not that it suits every use. Polyester satin is cheap and low-maintenance, and many pieces can go in the washing machine, though the care label decides. Silk needs a gentle wash.
Mulberry silk, momme and other silks
Mulberry silk is silk from Bombyx mori, which a 2023 study calls the most important producer of silk for centuries; our guide to mulberry silk covers it. Momme is a unit of fabric weight used for silk, explained in our guide to momme. Tussah, eri and muga come from other moths, and our overview of the types of silk describes them; under the EU definition, all of them are silk.
What our silk pillowcases are made of
The RENESSY silk pillowcases use 100% organic mulberry silk with a weight of 22 momme, and both faces of each case are silk. Mulberry silk comes from silkworms raised on the leaves of the mulberry tree, and momme measures the weight of silk fabric. The raw silk is rated grade 6A. Grade 6A is the top class in the Chinese raw-silk standard (GB/T 1797). GOTS, the Global Organic Textile Standard, certifies textiles made from organically grown fibres. The silk is GOTS certified. OEKO-TEX MADE IN GREEN is a label for textiles tested for harmful substances and made in traceable, certified production. The pillowcases carry the OEKO-TEX MADE IN GREEN label, and the label ID M27MNB1V9 can be checked on the OEKO-TEX website. The pillowcases carry the Dermatest 5-Star seal and the Dermatest Sensitive Skin seal, dermatologically tested for sensitive skin. A hidden YKK zip closes each case.
Frequently asked questions
Is mulberry silk real silk?
Yes, mulberry silk is real silk: it comes from Bombyx mori, the domesticated silkworm, and under the EU definition, silk is “fibre obtained exclusively from silk-secreting insects”.
Is satin natural or synthetic?
Satin is neither on its own, because it is a weave, not a fibre; a fabric sold simply as satin is often polyester or another synthetic fibre, and satin woven from silk is called silk satin.
Is viscose a natural fibre?
No, viscose is not a natural fibre: it is a manufactured fibre made from plant cellulose; EU law defines it as a regenerated cellulose fibre obtained by the viscose process.
Can a burn test prove that silk is real?
No, a burn test cannot prove that a fabric is silk, because it only places a fibre in a broad family such as protein fibres, and wool is a protein fibre too; a laboratory fibre analysis settles it.
Sources
- American Institute for Conservation, Textile Specialty Group. TSG Chapter V. Analysis and Testing Methods for Textiles, Section C. Fiber Identification. Conservation Wiki. https://conservation-wiki.com/wiki/TSG_Chapter_V._Analysis_and_Testing_Methods_for_Textiles_-_Section_C._Fiber_Identification
- Fletcher HM. Synthetic Fibers and Textiles. Kansas State College Agricultural Experiment Station. https://extension.k-state.edu/historicpublications/pubs/SB300.PDF
- Kunz RI, Brancalhão RMC, Ribeiro LFC, Natali MRM. Silkworm Sericin: Properties and Biomedical Applications. BioMed Research International. 2016;2016:8175701. doi:10.1155/2016/8175701
- Lee B, Pires E, Pollard AM, McCullagh JSO. Species identification of silks by protein mass spectrometry reveals evidence of wild silk use in antiquity. Scientific Reports. 2022;12:4579. doi:10.1038/s41598-022-08167-3
- Regulation (EU) No 1007/2011 of the European Parliament and of the Council of 27 September 2011 on textile fibre names and related labelling and marking of the fibre composition of textile products and repealing Council Directive 73/44/EEC and Directives 96/73/EC and 2008/121/EC of the European Parliament and of the Council, Articles 5, 7 and 16 and Annex I. https://eur-lex.europa.eu/eli/reg/2011/1007/oj
- Regulation (EU) No 1007/2011 as retained in UK law, Article 5 and Annex I. legislation.gov.uk. https://www.legislation.gov.uk/eur/2011/1007/article/5
- Schmidt T, Puchalla N, Schendzielorz M, Kramell AE. Degumming and characterization of Bombyx mori and non-mulberry silks from Saturniidae silkworms. Scientific Reports. 2023;13:19504. doi:10.1038/s41598-023-46474-5
- 16 CFR Part 303, Rules and Regulations under the Textile Fiber Products Identification Act, sections 303.6, 303.7 and 303.18. eCFR. https://www.ecfr.gov/current/title-16/chapter-I/subchapter-C/part-303
- University of Georgia Cooperative Extension. Understand Your Fibers. https://site.extension.uga.edu/textiles/textile-basics/understand-your-fibers/