Understanding Sustainable Textiles Through Climate-Adapted Traditional Crafts

Bashofu textiles have kept Okinawans cool and comfortable for more than 500 years. New study catalogues the science behind the craft.

For as long as humans have been around, we have been using our hands and senses to create beautiful and useful objects from the natural environment around us. While the artisans of old may not have the precision tools or scientific knowledge available today, their designs have nevertheless stood the test of time, and modern researchers and engineers are increasingly turning to these traditional crafts for inspiration on sustainable architecture, materials, and textiles.

Summers on the islands in Okinawa Prefecture are hot and humid. Today, we have AC systems – so how did Okinawans throughout history manage to stay cool and comfortable? One answer lies in the local design tradition. Houses are low and open plan behind thick coral or limestone walls, capturing a fresh breeze while staying protected from typhoon gales, and Okinawans have traditionally been dressed in Bashofu textiles. Bashofu kimonos stay both dry and cool while being remarkably soft, despite being woven from banana fibers which are notorious for their stiffness.

Recently, scientists have turned to Bashofu to learn what makes these sustainably produced textiles so well-adapted for comfort in the subtropics. In a paper now published in Scientific Reports, researchers from the Okinawa Institute of Science and Technology (OIST) have produced a comprehensive overview of how exactly the Bashofu materials and techniques alter the structural properties of the banana plant fibers to achieve the desired soft, durable, and breathable fabric. “Artisans have built up their intuition of how to create these textiles since at least the 16th century,” says study author Dr. Yoko Nomura from the OIST Science and Technology Group. “And now, we have grounded these intuitions in modern plant science.”

Bashofu fibers are obtained from the Okinawan Itobashou banana plant. The bottom right image is a zoomed-in portion at the white box in the upper image. The arrowhead on the close-up points to a handtied weaver’s knot. Unlike cotton fabrics, artisans manually tie the fibers in each of these knots by hand – and this is done 22,000 times for a single piece of kimono cloth. Scale bar on the upper photo is 10mm, lower is 1mm. © Koji Koizumi

Ensuring quality thread by thread, layer by layer, step by step

Central to Bashofu textile is the Okinawan banana, Musa balbisiana var. liukiuensis, or Itobashou, specifically the pseudostem (leaf sheath) of 3-year-old plants. At this age, the innermost fibers of the pseudostem, called Nahagu, are soft but strong enough to be woven. Moving outwards from the center, the increasing fiber age makes the threads stronger but less pliable, with the outermost leaf sheath before the external surface – Waha – being reserved for interior textiles. “The artisan uses the feel and color of the material to detect the difference in the individual fibers when separating out strands from the pseudostem,” explains Dr. Koji Koizumi of the OIST Scientific Imaging Section. Considering that fibers from at least 200 pseudostems are required for the creation of one high-quality kimono, this work calls for a high degree of efficiency on the part of the maker. “Our imaging analysis has shown that Nahagu fibers have significantly thinner cell walls than Waha fibers – something which is invisible to the naked eye. And yet, the artisans separate these threads based on touch and color, even discriminating between Nahagu fibers used for weft and warp,” says Dr. Koizumi.

Image analysis of Bashofu fibers. Top shows a cross-section of an Itobashou pseudostem, showing layers the Bashofu fibers are extracted from. a) is a photograph of different grades of Bashofu fibers, Waha being the toughest, used for interior textiles, and Nahagu being the softest, used for clothing. Nahagu can be further separated into Nuki and Hashi, used in weaving as the crosswise weft and vertical warp threads respectively. b-g) shows the typical cross-section of the fibers in the same order (b, Waha; c, Nahau; d, e, Nahagu Nuki; f, g, Nahagu Hashi), showing the clear differences in cell wall thickness that characterize each grade of fiber. Notice the honeycomb-like structure of the fibers which promote water diffusion, keeping the body cool by leading sweat away from the skin. h-k) are volumetric 3D projections based on stained microscopy images, showing the accumulation of residues (arrows) during the Bashofu process, which are absent in the finer Nahagu fibers (k). l-s) are scanning electron microscope (SEM) images of the surfaces of the fibers at a scale of 100 μm (top row) and 10 μm (bottom row). Notice the smoothness of Nahagu fibers compared to the other grades.

Bashofu involves 23 steps of processing Itobashou from stem to clothing, and while some efforts have been made to develop in-the-lab techniques to optimize the process, none have achieved the same level of quality. Instead, the research team hopes that through their scientific work to document the effects of each processing step on the fibers, test tensile strengths, and study the morphology of fiber cells with advanced scientific imaging, they can both help preserve the art of Bashofu for posterity and lay a foundation for future research into this unique, climate-adapted craft.

“We have a close relationship with the people who keep the art alive, and we are very thankful for the materials they have provided us with, considering how difficult they are to create,” says Dr. Nomura. “We have much to learn from Bashofu. The honeycomb structure of Bashofu fibers effectively leads sweat away from the skin through water diffusion, not to mention that both the process and product of Bashofu are highly sustainable. It is cultural as well as a scientific treasure that we want to help preserve.”

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