Sericin vs Fibroin: What Is the Difference? (2026)

Open a silk cocoon and you will find two proteins working together. One forms the strength. The other holds everything in place. In cosmetics, people often use the two names as if they meant the same thing. They do not.

In this guide, we explain what each protein is, how they differ, and which one fits which product. We make both kinds of ingredient in Ramanagara, Karnataka, so we also share what we see buyers confuse.

What is fibroin?

Fibroin is the structural protein of silk. It forms the long, strong fibre at the centre of every thread. It is the protein that gives silk its strength and its sheen.

For cosmetic ingredients, fibroin is broken into smaller pieces. These become silk peptide and silk amino acids. Whole fibroin can also be milled into a silk powder.

What is sericin?

Sericin is the gum-like coating around the fibroin fibre. It glues the threads together inside the cocoon. It is rich in serine, an amino acid that attracts water, and it dissolves in warm water. Our full explainer is in What is sericin?.

How do sericin and fibroin differ?

Which ingredients come from which protein?

• From sericin: Sericin Powder, Hydrolyzed Sericin and Hydrolyzed Sericin Solution.
• From fibroin: Silk Powder, Silk Peptide, Silk Peptide Solution and Silk Amino Acids.
• Combined: Silk Protein Complex blends molecular weights.

How to choose between them

1. Start with the product. Toners and serums suit smaller, lighter grades. Creams, masks and hair conditioners can use larger, film-forming grades. Makeup powders use silk powder.
2. Pick the effect you want. For a moisture-retaining film, look at sericin. For a soft, smooth feel, look at silk peptide or amino acids.
3. Compare two sizes. One smaller and one larger grade, in your own base.
4. Ask for documents. A data sheet, a certificate of analysis and a safety data sheet should come with the sample. See our guide to TDS, COA, SDS and INCI.

Common mix-ups

1. "Silk protein" means one thing. It does not. It covers several ingredients from two proteins.
2. Sericin is silk. Silk fibre is mainly fibroin. Sericin is the coating.
3. Hydrolyzed means better. It means smaller. Smaller suits light products, not every product.
4. Natural means vegan. Both proteins come from silkworm cocoons, so they are animal-derived.

Final thoughts

Fibroin is the strong core. Sericin is the water-loving coating. Choose by product type, then by size, and test in your own base.

Not sure where to start? Contact us with your product type and market, and we will suggest a grade.