The Luxury of Silk In Mattresses and Bedding
According to Chinese legend, sericulture, or silk production, originated in China during the reign of the Yellow Emperor in 3,000 BC when it was taught to the people by his wife, Lady Hsi-Ling-Shih, the goddess of silk. Archeological evidence, on the other hand, suggests that silk production might be twice as old, if not older. In 1924, silk eggs were discovered dating back to around 2300 BC. Later, silk ribbons were found dating back to around 3000 BC. More recently, an ivory cup with carvings of silkworms was found alongside sericulture tools. All date back to around 6,000 – 7,000 BC (1). These findings show that humans owe a longstanding loyalty to silk.
There are over 500 varieties of silk moth in the world, and an even crazier number of silk producing insects as well as arachnids (spider webs), but only three species of silk moth are used commercially. Those moths are Bombyx mori, Samia cynthia, and Antheraea pernyi. B. mori is a blind, flightless, domesticated moth and is not found in the wild. B. mori also has a very unique diet – it only eats the leaves of the mulberry tree. B. mori produces the most lustrous silk of the three. S. cynthia only eats the leaves of trees belonging to the Ailanthus genus or “The Tree of Heaven,” and has a coarse, yet more durable silk which is more affordable than B. mori silk. A. pernyi, or the Chinese tussah moth, is the one who lends his name to “wild silk,” which is commonly known as Tussah silk or Ahimsa silk. Wild silk is produced by any species of moth other than B. mori. (2)
Silk is made up largely from insoluble protein fibroin and protected by a coating of a water-soluble protective gum known as sericin (about 25-30% of raw silk protein). Silk proteins form into triangular prisms which allow the fiber to catch and refract light in many dazzling ways giving silk its notable shimmer. Most of the sericin (but not all) is stripped during processing and discarded as a pollutant, however, studies have shown some benefit to sericin. Sericin has proven to be antibacterial, UV resistant, oxidative resistant and possesses moisturizing properties. In cases where sericin was separated from the degumming liquor, this biomolecule mixed well into creams and shampoos to make them more moisturizing and was blended into textiles, making them more resistant to molds, bacteria, and overall wearing (5). Some websites I stumbled across that talked up their silk sheets even indicated that the sercin left behind in the silk offered restorative, anti-aging properties to the user.
Despite less expensive, synthetic fabrics such as rayon appearing in the world, silk production has doubled over the last thirty years, with about fifty percent of all silk originating out of China and Japan (1). This increase in demand is due to several factors. One being that silk is smooth to the touch without being slippery like its synthetic counterparts. It is one of the strongest fibers produced by nature and silk only loses 20% of its strength when fully saturated as opposed to rayon’s 75%. Silk is not particularly flexible, however, and when forced to stretch tends to stay stretched, whereas rayon has a nicer bounce-back, especially when married with polyester and spandex. Both rayon and silk are prone to shrinkage and dry cleaning is recommended over machine washing. Silk is also a poor conductor of electricity and is prone to static cling unlike rayon (2). However, this low conductivity is also a good thing as it keeps warm air close to the skin in low temperatures, and its high absorbency makes it a favored fabric for hot places and for physical exertion, since as the fabric absorbs moisture it becomes cooler.
Silk production has seen a rise in criticism in the 21st century since the silkworm is typically killed in the extraction process and is then later eaten or used in fish food. For this reason, the industry has seen an upswing in wild silk, which is produced largely by S. cynthia and A. pernyi. These two species of moth cannot be cultivated in a domestic setting, and therefore most of these cocoons have already been vacated by the time they are retrieved. When a moth is ready to escape its cocoon, it produces a chemical that fills the cocoon and bores a hole in one side so that it may escape. This chemical damages some of the silk fibers resulting in shorter strands. Long-fibered silk from a B. mori (which was not allowed to complete metamorphosis) is reeled when processed, while short fibers from S. cynthia and A. pernyi are spun (7).
I do not know whether the mattress industry as a whole tends to use more domestic silk or if they prefer wild silk for their products. I spent a sizeable amount of time looking for this information and had this vague memory in the back of my head of one of our sales reps telling me the industry tends to use a method of silk extraction that doesn’t kill the worm. Could it be possible that mattresses prefer wild silk instead of domestic silk? It certainly makes the most sense looking at the processes involved in their making. When a B. mori caterpillar weaves its cocoon, it uses one continuous line of silk for the entire process. When the cocoons are later boiled, the end of the silk string is found and the cocoon carefully unspun. One cocoon can reach over 3,300 feet, meaning it would take only ten cocoons stretched vertically to reach the height of Mount Everest! These long fibers are then spun together, requiring up to ten individual silk fibers to make one silk “thread.” Wild silk, since it has been damaged by the emerging moth, has been severed into many short fibers, and is, therefore, a better contestant for “loose fiber” silk/wool blend (which is what we have in many of our natural mattress lines). This is all speculation, of course, all I do know is that every ingredient that goes into our US made mattress is OEKO-TEX Ⓡ certified. OEKO-TEXⓇ will be further expounded upon in my piece on latex.
In sum, silk is one of the strongest fibers generated by nature. It’s excellent at cooling a body down, is highly absorbent, and is smooth to the touch without being slippery. The sericin that remains in the silk after degumming is believed to have restorative properties and is naturally antimicrobial. There are two types of silk, domestic and wild, and it’s not entirely far-fetched to believe our mattresses use wild silk for their filler. Silk not only adds to a products story of longevity, but also to its breathable, temp-regulating story.