Silk comes from silkworms, specifically the cocoons they spin when preparing to transform into moths. The most common source is the domesticated mulberry silkworm (Bombyx mori), which produces roughly 90% of the world’s commercial silk. China is the single largest producer and supplier, followed by India, with smaller contributions from Uzbekistan, Brazil, and several other countries.
How Silkworms Make Silk
Silkworms don’t produce silk from their skin or from something they eat. They manufacture it inside a pair of specialized silk glands that run along the length of their bodies. These glands have three distinct sections, each with a different job. The rear section synthesizes the core silk protein, called fibroin. The middle section stores that fibroin and adds a sticky coating protein called sericin. The front section is where the liquid silk transforms into a solid fiber as it flows toward a tiny nozzle on the worm’s head called a spinneret.
The finished silk fiber has a simple structure: two filaments of fibroin protein running side by side, wrapped in a sericin coating that glues them together. Each silkworm produces one continuous thread that can stretch over a kilometer long, winding it around itself over several days to form a cocoon. This happens at the end of the larva’s fifth and final growth stage, just before it would normally pupate and emerge as a moth.
From Cocoon to Fabric
Turning a cocoon into usable silk involves several steps. First, the cocoons are “stifled,” meaning they’re exposed to hot air at around 60 to 70°C for several hours. This kills the pupa inside and prevents it from breaking through the cocoon wall, which would sever the continuous thread. In conventional production, this step happens as quickly as possible after the cocoon is complete, often within about 15 minutes of collection.
Next comes reeling. The cocoons are soaked in hot water to soften the sericin coating, which loosens the filament so it can be unwound. Because a single filament is extremely fine, workers combine filaments from four to eight cocoons simultaneously, twisting them together into one stronger silk thread. This combined thread is wound onto reels while maintaining consistent tension and speed to produce an even yarn.
The raw silk at this stage still has its sericin coating, giving it a somewhat stiff, dull quality. A later process called degumming removes the sericin through boiling in a mild alkaline solution, revealing the smooth, lustrous fibroin fiber underneath. From there, the silk can be dyed, woven, and finished into fabric.
Four Major Types of Silk
Not all silk comes from the same worm or has the same qualities. The four most commercially important types each come from a different species of silkworm feeding on different plants.
- Mulberry silk comes from domesticated Bombyx mori caterpillars fed exclusively on mulberry leaves. It’s the smoothest, most lustrous, and strongest silk fiber, used for luxury bedding, scarves, and formal clothing.
- Tussar silk is produced by wild Antheraea mylitta silkworms living in forests and feeding on oak and other tree leaves. It has a natural golden color and a more textured feel, commonly used in sarees and upholstery.
- Eri silk comes from Samia ricini caterpillars that feed on castor plants. It’s softer and warmer than mulberry silk, and notably, it can be harvested after the moth emerges naturally, making it popular in sustainable fashion.
- Muga silk is the rarest variety, produced by Antheraea assamensis silkworms that only thrive in the forests of Assam, India. Experts have tried relocating these worms to other regions, but they simply don’t adapt. Muga silk has a distinctive natural gold color that becomes richer with age, making it prized for heirloom garments.
Peace Silk and Ethical Alternatives
Standard silk production kills the pupa inside the cocoon, which raises ethical concerns for some consumers. Peace silk, also called Ahimsa silk, takes a fundamentally different approach. Instead of stifling the cocoons immediately, producers collect them carefully and wait 10 to 14 days for the pupa inside to complete its transformation into a moth. The moth then breaks through the cocoon wall using a special enzyme and emerges naturally.
The tradeoff is practical. When the moth exits, it leaves a hole in the cocoon that breaks the continuous silk filament into shorter pieces. These shorter fibers must be spun together like cotton rather than reeled as one long thread, producing a silk with a slightly different texture. The process also takes significantly longer, adding roughly 10 days compared to conventional methods, which raises the cost.
Lab-Grown and Synthetic Silk
A newer source of silk doesn’t involve any worms at all. Biotech companies are now producing silk-like proteins through fermentation, similar to how beer is brewed. The Japanese company Spiber, for example, developed a method to produce spider-silk-like proteins by designing new amino acid sequences and introducing the altered DNA into microorganisms. These microbes then churn out silk proteins in large fermentation tanks, which can be spun into fibers.
Spiber’s product, called Brewed Protein, has a lower environmental impact across its lifecycle compared to petroleum-derived fabrics like nylon and polyester. While these bio-engineered silks are still scaling up to compete with traditional silk on price and volume, they represent a growing category that avoids both animal welfare concerns and the environmental footprint of synthetic textiles.