Why Is It Light and Fluffy? The Secret of Asano Nenshi's "SUPER ZERO®" Lies in "Dissolving Thread"

By creating hollow spaces inside the thread to trap air, Asano Nenshi's proprietary material "SUPER ZERO®" achieves astonishing volume and lightness. Starting with the towel line "エアーかおる", it is now used in denim, knitwear, and outer shell fabrics for down jackets.

The key to creating these unique properties lies in twisting water-soluble yarn with natural fibers, and then "dissolving" the water-soluble yarn later during the processing stage. How does dissolving yarn create such lightness and volume? We asked Kosuke Asano, Senior Managing Director of Asano Nenshi, to explain the mechanism and technology behind it.

The principle behind "SUPER ZERO®" lies in using water-soluble yarn.

Water-soluble yarn developed by Kuraray is tightly twisted in the opposite direction with natural fibers such as cotton, wool, and linen. When only the water-soluble yarn dissolves during the dyeing and finishing processes, hollow spaces are created inside. A spring-like structure remains inside the yarn, trapping a vast amount of air.

Originally, what Asano Nenshi aimed for with "SUPER ZERO®" was the elasticity brought by these hollow spaces. Applying their specialty technology of twisting polyurethane with cotton yarn to produce stretch yarn, development began with the goal of achieving natural stretch without using rubber.

"When the water-soluble yarn dissolves, that portion becomes a hollow space, leaving behind a spring-like structure. By applying our existing technology that provides stretchability without relying on polyurethane, we started developing yarn with natural stretch properties."

However, another property of this yarn was discovered purely by chance. When they asked a towel manufacturer in Mie Prefecture to produce a prototype stretch towel, "SUPER ZERO®"—which was originally instructed to be used in the ground weft—was instead used in the pile loops due to local towel industry practices.

The finished towel had no elasticity. Yet, it exhibited unexpected characteristics: the yarn had impressive volume, high absorbency, and was soft yet light.

"We had never seen a towel like that before. The yarn had volume, and the absorbency was far higher than normal. Despite being soft, it produced very little shed lint, and because it trapped so much air, it felt remarkably light. It truly combined the best of all towel qualities."

The hollow spaces created to generate elasticity turned out to deliver volume, lightness, and absorbency as well. This was the exact moment they realized the new possibilities of this yarn.

Even after understanding its properties, mass production was another story. The biggest hurdle in development lay in the final stage of the twisting process.

High-twist yarn untwists if left as is, making it impossible to weave or knit. Therefore, steam setting is applied to fix its shape using steam. Asano Nenshi, which specialized in fine yarns, possessed steam-setting equipment—a rarity for a yarn-twisting factory.

However, "SUPER ZERO®" was combined with a yarn that dissolves in water.

"Normally, if you apply steam setting, the water-soluble yarn dissolves at that stage. But if it dissolves here, the yarn loses its strength, making it impossible to weave or knit. Setting the yarn without dissolving the water-soluble component—that was the hardest part."

Fixing the shape securely without dissolving the yarn. Making matters even more difficult was the fact that heat did not reach the core of the yarn uniformly.

"We struggled immensely to address the incomplete state where the outer layer was set, but the inner core was not."

They repeatedly modified the steam setter, fine-tuning the temperature and timing. It took three years just to develop the yarn, and five years in total including commercializing the towel. Even after commercialization, the issue of partially dissolved yarns sticking together during steam setting persisted.

By conventional logic, it was a contradictory and daunting challenge. "Our president at the time said, 'Treasures are not buried in common sense. We won't survive unless we do something unconventional,'" Asano recalled fondly.

"SUPER ZERO®" comes in two types: one using the water-soluble yarn "Mintval" and another using "425," which uses starch-coated yarn. "425" was developed to enable yarn-dyeing, which was difficult to achieve with water-soluble yarn. Since then, a technique for yarn-dyeing Mintval was also established, and development is currently focused on the Mintval-based type.

"Type 425 offers more volume than standard 'SUPER ZERO®' made with Mintval. However, because it incurs higher costs, we are currently focusing our efforts on developing the Mintval type."

There is solid numerical data to back this up. In tests using a perspiration simulator at the Gifu Prefectural Industrial Technology Center, skin temperature when wearing the fabric was 0.7°C lower compared to untreated items. The test generated simulated sweat and measured the entire process through to evaporation.

The mechanism starts with high water absorbency. The more water it absorbs, the faster the evaporation, making it easier for heat of vaporization to lower skin temperature.

However, Asano remains cautious about its functionality in summer. In situations with continuous sweating, other factors come into play with cotton. Instead, he notes that the benefits are even clearer in winter.

"In winter, air warmed by body heat is trapped within the hollow spaces, providing exceptional thermal insulation."

Currently, combining this technology with wool is drawing significant attention. Shrink-resistant wool used in innerwear and T-shirts can sometimes lose its soft texture through processing. Applying the "SUPER ZERO®" process restores softness and reduces scratchy skin irritation.

The applications of "SUPER ZERO®" extend far beyond towels. Collaborating with textile trading company STYLEM TAKISADA-OSAKA gave a major boost to its expansion into apparel.

For yarn manufacturer Asano Nenshi, proposing yarn characteristics in the form of fabric and holding fabric inventory required for mass production posed major hurdles. Thus, Asano Nenshi supplies the yarn while STYLEM handles fabric design, development, and inventory management, creating an environment that makes it easy for apparel brands to adopt.

Denim is leading the way in this expansion. By incorporating "SUPER ZERO®," fabric retains an authentic denim look while achieving softness and lightweight comfort. It has already been adopted by prominent domestic denim brands.

"Despite being denim, it is overwhelmingly soft and light. Today's market demands softness even in denim, so it aligned perfectly with those needs."

Furthermore, a global luxury brand took notice of "SUPER ZERO®" used in the weft of denim shirt fabric, leading to its adoption for the shell fabric of down jackets. This season, it is also expanding into knitwear.

Water-soluble yarn is tightly twisted with natural fibers, and then only that water-soluble yarn is dissolved in a later process. The resulting hollow spaces give the yarn volume and lightness, translating into functional benefits like high absorbency and heat retention. Discovered through towels, these features are now expanding into denim, down outerwear, and knitwear.

Achieving this structure required overcoming the hurdle of "steam setting"—setting a tight twist without dissolving the water-soluble yarn. Rather than "adding" material to yarn, creating hollow spaces by later "removing" a twisted-in thread creates functionality. This innovative technology, "SUPER ZERO®," is the fruition of Asano Nenshi's relentless dedication to craftsmanship.