The Process and Benefits of Creating Spun Silk

Every year, silk reeling units across Asia generate substantial quantities of waste – broken filaments, damaged cocoons, and unusable outer layers that cannot be turned into premium reeled silk. Rather than discarding this material, the sericulture industry has developed a well-established method to recover its value: spinning it into spun silk. This process transforms what would otherwise be written off as by-product into a commercially useful, genuinely versatile yarn. Understanding how spun silk is made – and why it matters – offers a clear picture of resource efficiency in one of the world’s oldest textile industries.

What is spun silk and how is it different from reeled silk? 🔗

Reeled silk is produced by unwinding the continuous filament from a cocoon in one long thread. It is smooth, highly lustrous, and strong. Spun silk, by contrast, is made from the shorter fibers that cannot be reeled. According to Treenway Silks, spun silk is produced from the cocoon fibers that remain after initial reeling – the weak filaments from the outer and inner layers of the cocoon, along with damaged, discoloured, or imperfectly shaped cocoons that serve as raw material for the spinning process.

The FAO Silk Reeling and Testing Manual confirms that rejected cocoons and reeling waste are reprocessed into spun silk yarns. The result is a yarn that is softer but less lustrous, less strong, and less elastic than reeled silk – yet it still carries all the fundamental properties of silk: breathability, light weight, and a pleasant handle. As documented at a reeling mill in India, the short filaments are aligned, brushed, and spun into schappe yarn, with further by-products processed into the coarser bourette yarn.

Raw materials for spun silk production 🔗

Spun silk draws its raw material from several categories of silk waste generated during normal reeling operations. These include:

Reeling waste: According to FAO’s silk reeling data, the total filament length of a cocoon ranges from 600 to 1,500 metres, of which only about 80 percent is reelable – the remainder is removed as waste. This includes the brushing waste from the outer layer of the cocoon and the innermost filaments closest to the pupa, which are too weak or irregular to reel.

Unreelable cocoons: Not all cocoons in a batch are suitable for reeling. Damaged, crushed, broken, undersized, or double cocoons are set aside during sorting. Cocoons whose pupae have died before harvest, and those stained by adult moths, also fall into this category. The FAO manual notes that pierced cocoons – those from which the moth has already emerged – and end-missing cocoons are among the primary inputs for spun silk processing.

Eri silk cocoons: Eri cocoons are a special case. As recorded by the Directorate of Sericulture, Assam, Eri cocoons have an open-mouthed structure with a discontinuous filament, making them entirely unsuitable for reeling – they are suitable only for spinning. Approximately 90 percent of Eri cocoons are hand spun in Assam, India.

The spun silk manufacturing process 🔗

Spun silk production is a dry spinning process – unlike reeling, which is done in water. The steps follow a defined sequence that progressively cleans, aligns, and refines the short silk fibers into usable yarn.

1. Degumming 🔗

The collected waste is first degummed to remove sericin, the protein gum that binds silk filaments together. Per silk spinning documentation from the University of Mysore, the wastes are boiled at 90-95°C for about one hour using a soap and soda ash solution (typically soap at 22.5% and soda at 6.25% for mulberry cocoons), then washed repeatedly and dried. The silk is then conditioned – kept in a conditioning room for around 15 days to reabsorb approximately 11% moisture, bringing all waste types to a uniform state before further processing.

2. Mixing and opening 🔗

Different types of degummed silk waste are blended together to achieve uniform quality and consistent process performance. The mixed material is then passed through an opening machine, which has fork-like structures that separate the tangled mass of fibers into a more ribbon-like form with roughly parallel filaments. Batches are typically made in 200-250 gram balls.

3. Filling, pegging, and combing 🔗

The opened material passes through a filling or pegging machine – a drum studded with rows of combs – that delivers a continuous sliver. This is followed by combing or dressing, which is the most critical step: it eliminates short fibers and parallelises the long ones. The short fibers removed during two to four rounds of dressing are not discarded – they are collected separately for the production of noil yarns, used in carpet manufacture and other coarser applications.

4. Drawing and roving 🔗

The combed slivers are then passed through a series of six drawing machines, each stretching the material at a draft ratio of 1:6 to 1:10. This drawing stage is also where blending occurs – slivers of silk can be combined with slivers of other fibers such as polyester at this point. The drawn sliver then goes to a roving frame, where it is further attenuated, parallelised, and given a slight twist to form the roving ready for the spinning frame.

5. Spinning, gassing, and finishing 🔗

On the spinning frame, the roving is drawn to the required yarn count, twisted, and wound onto bobbins. Two or three single spun yarns are then doubled and twisted together for additional strength. To improve lustre and appearance, the yarn is gassed – passed through a clear flame at 500-600 metres per minute to burn off protruding surface fibers. Final cleaning removes the burnt particles, and the yarn is reeled into standard-sized hanks, skeined, bundled, and packed into bales.

Grades of spun silk: schappe and bourette 🔗

Spun silk is commercially available in two main grades. As textile classification sources note, both are produced using special machinery broadly similar to cotton and worsted spinning systems.

Schappe silk is the higher-quality grade. It is made from longer fibers after intensive combing, which aligns the fibers tightly and produces a smooth, consistent yarn with considerable sheen. Among the three types of spun silk, schappe has the greatest smoothness and sheen. It is used in fine apparel fabrics, linings, and pile fabrics.

Bourette silk is produced from the shorter fibers that remain after schappe processing. Bourette is matte and coarser in texture, with an irregular, knotty surface because residual sericin cannot be fully removed from its very short fibers. Despite its lower sheen, bourette is more voluminous, warmer, and durable than finer silk types – its rough, bumpy texture makes it a recognised fashion fabric valued for its distinctive appearance. In Ayurvedic applications, its high sericin content is considered to have anti-inflammatory properties.

Uses of spun silk yarn 🔗

According to FAO’s by-products utilisation documentation, spun silk is used for shantung, pile fabrics, dress trimmings and linings, elastic webbing, sewing silk, summer-weight silks, velvets, umbrella fabrics, and insulation. The yarn can be used on its own or blended with other fibers. During the drawing stage, silk slivers are routinely combined with synthetic fibers such as polyester to produce blended yarns suited to both warp and weft. When blended with wool, silk improves the wool’s smoothness and drape; when blended with cotton, it adds lustre and softness.

Industry research on silk waste utilisation also identifies spun silk as a raw material for insulation fabric – its protein structure provides resistance to temperature fluctuations and moisture-wicking properties that make it suitable for outdoor and functional textiles.

Contribution to sustainability in sericulture 🔗

The production of spun silk is fundamentally a waste recovery process, and its role in making sericulture more resource-efficient is well documented. A 2025 study in the journal Sustainable Production and Consumption found that production waste such as low-grade cocoons can be repurposed into textiles, offering both environmental and economic benefits as part of a shift toward circular practices in the silk industry.

A comprehensive review of sericulture by-products highlights that floss silk, noil, and short fibers are repurposed into spun yarn, nonwoven fabrics, upholstery, and insulation materials – recognising these outputs as valuable co-products rather than waste enhances economic viability and supports environmental sustainability. The same review notes that with appropriate processing technologies, sericulture by-products can contribute to a zero-waste industry model.

In India, this principle is already in practice. The Directorate of Sericulture, Assam notes that about half the silk in each muga cocoon that can be reeled is taken as raw silk, while the remainder – the waste noil – is further processed into spun silk. All cocoons produced are converted into silk yarn and fabric within the state, with efforts ongoing to reduce high production costs by utilising reeling wastes and producing value-added products.

Research published in Fibers (MDPI) points out that the textile industry typically generates production waste amounting to up to 25% of raw material input. Channelling silk waste into spun silk production directly addresses this, turning an industry-wide challenge into a commercially productive output.

Properties and limitations of spun silk 🔗

Spun silk retains most of the core qualities that make silk desirable – it is breathable, lightweight, soft against the skin, and has natural antibacterial properties. However, there are trade-offs inherent to its structure. The FAO manual states clearly that spun silk has less strength and elasticity than reeled silk because of the shorter staple used. Fabrics made from spun silk will gradually become fuzzy with wear, as the short fibers tend to pill on the surface over time – a characteristic absent in reeled silk fabrics.

Spun silk is also less expensive than reeled silk, making it accessible for a wider range of textile applications where the premium lustre of reeled silk is not essential. The cost of production, while lower than reeled silk, still includes the collection, degumming, and multi-stage spinning of waste material – processes that require controlled conditions and skilled operation to maintain consistent yarn quality.

What do you think? Given that spun silk recovers value from material that would otherwise go to waste, do you think more textile industries should adopt similar by-product utilisation systems? And with growing global interest in sustainable fashion, could spun silk find a larger mainstream market than it currently occupies?

References

1. https://www.treenwaysilks.com/kc-yarnsblends.php
2. https://www.fao.org/4/x2099e/x2099e09.htm
3. https://www.sartorbohemia.com/article/22/how-silk-is-made-reeling-mill/
4. https://www.fao.org/4/x2099e/x2099e03.htm
5. https://sericulture.assam.gov.in/portlets/silk-reeling-and-spinning
6. https://hbmahesh.weebly.com/uploads/3/4/2/2/3422804/silk_spinning.pdf
7. http://textileengg.blogspot.com/2015/11/different-types-of-silk.html
8. https://peggyosterkamp.com/2022/07/silk-is-silk-is-silk-or-not-a-guest-post-by-giovanna-imperia/
9. https://www.langyarns.com/en/Stories-by-LANGYARNS/Blog/Blog-post/114-Silk-/
10. https://en.wikipedia.org/wiki/Bourette
11. https://ijariie.com/AdminUploadPdf/SILK_WASTE_GENERATION_AND_ITS_PRODUCTIVE_UTILIZATION_ijariie25790.pdf
12. https://www.sciencedirect.com/science/article/pii/S2352550925000582
13. https://www.agronomyjournals.com/archives/2025/vol8issue8S/PartF/S-8-8-42-306.pdf
14. https://www.mdpi.com/2079-6439/11/6/56