What is silk made of?
To understand how silk is formed, we must first study its chemical composition. Silk is a natural protein fiber that is biologically similar to human hair or wool, but it has a unique crystal structure, which gives it a famous luster.
Two key proteins: silk fibroin and sericin
Silk is mainly composed of two proteins secreted by silkworm:
Fibroin (70-80%): This is the structural center of silk thread. It is composed of layered anti-parallel β-sheets, giving the fiber amazing tensile strength and rigidity.
Sericin (20-30%): This is a ‘colloid’ or sticky coating that binds two silk fibroin fibers together. It protects the cocoon, but is usually removed during processing to reveal the shiny fibers below.
Do you know? The triangular prism structure of silk fiber enables it to refract incident light at different angles, resulting in the effect of color change, which is what we call ‘lustre’.
Where does silk come from? Overview of Historical Geography
The history of silk is closely related to the history of human civilization.
Originated in ancient China
Legend in about 2700 BC, China’s Leizu (Leizu, also known as Xilingshi) in drinking hot tea, a cocoon fell into her cup. As she tried to remove it, the hot air untied a long, delicate thread. Whether legends or facts, archaeological evidence confirms that silk production (i.e., sericulture) originated in Neolithic China.
For thousands of years, China has guarded the secrets of silk production under the deterrent of the death penalty. It was not until the opening of the Silk Road around 130 BC that this fabric began to spread to the West and eventually reached Rome, when its value was comparable to gold.
Modern Silk Center
Today, although silk is produced in more than 60 countries, most of the world ‘s production still comes from Asia:
China: the world ‘s largest producer (about 80 % of global supply).
India: the second largest producer, known for its brightly colored sari and wild silk (such as tussah silk).
Uzbekistan, Brazil and Thailand: important regional producers with a unique weaving tradition.
How is silk formed? Biological processes
The creation of silk began in the life cycle of silkworm. Strictly speaking, ‘silkworm’ is not a worm at all, but a caterpillar larva of Bombyx mori.
- Larvae stage
After hatching from tiny eggs, the caterpillars greedily feed for about 35 days. Its diet consists entirely of fresh mulberry leaves. During this period, its body size will grow to about 10,000 times the original, and molt four times.
- Cocooning
Once mature, the silkworm will stop eating and prepare to spin cocoons. It has two specialized glands to produce liquid filaments.
- The silkworm squeezes the liquid protein through a tiny opening in its head called a ‘spinneret’.
- When the liquid touches the air, it will instantly harden into a solid filament.
- The silkworm moves its head in an ‘8’ shape, wrapping a continuous silk thread about 1 km (3, 000 ft) long around itself.
- This process takes 3 to 8 days.
How is silk processed? Step-by-step guide
From the original cocoon to the elegant skirt, this transformation involves a meticulous, labor-intensive process, known as silk reeling process. The following is a seven-step tour of silk processing.
Step 1: Harvest and cocoon selection
Once the cocoon is completed, it needs to be harvested. Farmers must be carefully classified according to color, shape and size to ensure that the final thread is uniform. Flawed cocoons are usually used for low-grade silk or as fillers for silk quilts.
Step 2: Cocoon drying
This is the most controversial step in traditional silk production. In order to prevent the moth from breaking the cocoon (which breaks the continuous silk thread), the cocoon is subjected to heat treatment – usually steam or hot air. This will kill the pupae inside and dry the cocoons for storage.
Note: For people seeking non-cruel options, ‘Ahimsa Silk’ or ‘Peace Silk’ allows moths to hatch before processing, but this can lead to thread breakage, reduced gloss, and must be spun like wool.
Step 3: degumming (cocoon cooking)
The cocoons were immersed in boiling water. This softens the sericin that binds the fibers together. Without this step, the thread will be too rough and fragile to unravel.
Step 4: Reeling
Finding the thread head of a thread is a delicate task. Once found, silk threads from multiple cocoons (usually 4 to 8) are usually grabbed together and unwound onto the reel.
Why merge them? The single fiber is too thin to use. By rolling several strands together, they will bond (due to the residual softened sericin) into a cohesive raw silk thread.
Step 5: Twisting (Throwing)
‘Twisting’ is an industrial term, meaning throwing. This twists the raw silk strands to increase strength and prevent wear.
Organzine: made by twisting the threads in one direction, then merging them and twisting them in the opposite direction. Warp for fabric (vertical line).
Tram: silk thread that is only slightly twisted. For weft (horizontal line).
Step 6: Dyeing
At this stage, the yarn is boiled again to remove the remaining sericin. This will reduce the weight by about 25 %, but leave incredibly soft and white silk, ready to accept dyes. Silk absorbs dyes more than almost any other natural fiber, resulting in gorgeous, deep colors.
Step 7: Weaving
Finally, the dyed yarn is woven into a fabric on the loom. The type of weave determines the final texture:
Charmeuse: satin weave, front bright, back dark.
Chiffon: plain weave, transparent and light.
Crepe de Chine: Twisted fibers produce cobblestone-like textures.
Silk vs. Synthetic alternatives
In order to give readers a clear understanding of the differences between silk and synthetic substitutes, Silkyue compares the two and makes the following comparison table.
| Table of comparative synthetic alternatives for silk | ||
|---|---|---|
| Feature | Silk | Synthetic Silk (Polyester/Rayon) |
| Origin | Insect protein (Silkworm) | Petroleum or Wood Pulp |
| Breathability | High (Temperature regulating) | Low (Traps heat) |
| Texture | Soft, waxy, warms to body temp | Slick, slippery, can feel plastic-like |
| Flammability | Self-extinguishing (burns to ash) | Melts and smells like plastic |
| Cost | High | Low |
Is silk production sustainable?
Silk is a renewable and biodegradable resource. Mulberry (food source) requires less pesticides than cotton crops. However, the high water consumption during processing and the ethical issues about silkworms are debatable views.
How to distinguish silk?
‘Combustion test’ is the gold standard. Pull out a loose thread and ignite it.
Silk: Burning slowly, smells like charred hair and leaves pinchable black ashes.
Filament: Melt quickly, smell like plastic, and leave a hard bead.
Why is silk so expensive?
It takes about 2,500 to 3,000 cocoons to produce a yard of woven silk fabric. The process relies heavily on manual labor and time-consuming farming (sericulture), which proves that its high price is reasonable.
Expanding Reading
Explore different types of silk
Although mulberry silk is the most famous, the world of sericulture provides silk of various textures and colors produced by different moths.
Mulberry Silk
This accounts for 90% of global production. It is the most fine, smooth and uniform type. Because silkworms are fed on mulberry leaves only under artificial rearing, the silk produced is pure white and incredibly tough.
Want to learn more about mulberry silk? Please check out this article: What is Mulberry Silk? A Complete Guide to the Finest Silk Fabric
Castor silk/Eri Silk
Also known as ‘Endi’ or ‘Errandi’, it comes from Samia ricini. Unlike mulberry silk, the processing of this silk usually does not kill the silkworm (the moth spins an open cocoon). Textures like wool and cotton make it heavier and warmer – very suitable for winter shawls.
Tussar silk/wild silk
Produced by moths (such as Antheraea mylitta) living in wild forests in India and China, tussah silk has a natural gold or copper color. Its texture is rougher and less durable than mulberry silk, but it is highly praised for its primitive and rustic beauty.
Muga Silk
Unique to the Indian state of Assam, Mugas is known for its natural golden color. It is very durable – often longer than the wearer ‘s life! It is traditionally reserved for the royal family and cannot be bleached or dyed because its natural luster is its main attraction.
Spider Silk
Although not yet commercially available for textiles, scientists are fascinated by spider silk because of its extremely high tensile strength (stronger than Kevlar fiber). Studies are currently underway to synthesize this protein structure for medical and industrial use.
Related Articles
Silk vs. Polyester: Why choose silk products?
What is silk? Is silk breathable?
What Is the Difference Between Satin And Silk?
How to Wash Silk and Remove Stains and Wrinkles
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