Water-Repellent Even After 100 Washes! How Did Asakura Senpu's "Dewelry®0" Overcome the Weakness of Fluorine-Free Technology?

When inspecting water-repellent fabrics, it is a crucial step for inspectors to wear gloves. Touching fabric with bare hands transfers trace amounts of sebum, causing those specific spots to lose water repellency and leave stain-like marks. Non-fluorine water-repellent finishes, which are expanding due to regulations on PFAS (per- and polyfluoroalkyl substances), have long faced the challenge of being "vulnerable to sebum."

Developed by Asakura Senpu, a dyeing and finishing manufacturer based in Kiryu City, Gunma Prefecture, "dewelry®0" is a PFAS-free processing technology that resists performance loss even when touched, maintaining Grade 4 water repellency even after 100 washes. How did a finishing manufacturer unable to formulate its own chemical agents reach this breakthrough? We spoke with Gotaro Asakura, Representative Director and President, and Yasuo Kogure, Technical Advisor in charge of development.

The origins of Asakura Senpu's water-repellent technology trace back to cloth diaper covers in the 1980s. Ordinary fabric allowed leaks, while vinyl-like waterproof sheets trapped moisture, causing diaper rash on babies. What was needed was a material that kept messes inside without becoming stuffy. The solution they arrived at was not "waterproofing," which covers the fabric's surface with a film, but "water repellency," a technology that repels water without clogging the weave.

As the spread of disposable diapers reduced demand for diaper covers, the company began applying its technology to racing swimsuits in the early 1990s. "A swimsuit that absorbs water becomes several times heavier—it's like swimming while wearing weights. If it doesn't absorb water, swimmers can stay light, and because water rolls right off the fabric, friction resistance between the body and the water is reduced," Asakura explains.

Competitive swimwear rules prohibit covering the fabric's surface with films such as plastic or rubber. A water-repellent technology that repels water powerfully without using a film became a major competitive edge for the company in this field as well.

What shook the very assumption of water-repellent processing was global regulations on PFAS. Certain PFAS chemicals do not easily decompose in the environment, raising concerns about accumulation in the human body as well as health and environmental impacts, leading to tighter regulations in places like Europe. "With regulations tightening worldwide, pushing back wouldn't solve anything. We had to recreate our previous water-repellent performance without using fluorine," says Asakura.

However, non-fluorinated water repellents shared a common, almost fatal weakness: the lack of "oil repellency" to repel oils. Maintaining water-repellent functionality was also difficult. "The entire industry is struggling immensely," Asakura explains. In the company's early non-fluorinated processing tests, spraying water onto fabric touched by bare hands and leaving it to sit caused the exact shape of the hand to appear as a wet mark.

The company interviewed nearly all of the roughly 20 domestic manufacturers of non-fluorinated water repellents available in Japan. The goal was not to compare competitors, but rather "to see if there was even a single chemical with oil-repellent properties." The result, however, was zero—not a single one was found.

Thousands of Commercial Chemical Combinations: Nearly Three Years of Relentless Experimentation

Because Asakura Senpu is not a chemical manufacturer, all usable chemicals were limited to commercially available products. Therefore, the company sought a breakthrough by optimizing the combination of water repellents and "cross-linking agents" that bond the water repellent to the fabric. In some cases, they even blended two types of water repellents. Procuring unreleased products and chemicals still under development, they repeatedly conducted tests with varying blending ratios.

The number of combinations tested exceeded thousands. Kogure and his assistant worked almost exclusively on the project over a research period of roughly three years. Even so, there were no setbacks in spirit. "Our goal was clear: to create something with the exact same functionality as fluorine," Kogure emphasizes with firm resolve.

Within the scope of Asakura Senpu's search, no non-fluorinated water repellent offered the required oil repellency. If that was the case, why not prevent sebum from touching the water repellent directly? The approach they arrived at was creating a special structure on the fabric surface through clever processing. The model they emulated was the ultimate ideal of natural water repellency: the "lotus leaf."

"We had no choice but to use commercially available water repellents. So, we somehow found a processing method that prevents sebum from making direct contact," says Kogure. While physically scratching the surface to create micro-scale unevenness was an option, pressure during wear would crush the ridges and destroy performance. Instead of taking that route, the company replicated the structure using a proprietary processing method.

The results are evident in the numbers. Even after sebum is applied, "dewelry®0" fabric maintains a high standard with a contact angle of 151.79° and a sliding angle (at which water droplets roll off) of 12.62°.

Resistance to sebum was a non-negotiable requirement for the company. Many of its products are items handled frequently by hand, such as furoshiki (wrapping cloths), where sebum marks are easily noticeable. Their uncompromising commitment—"We absolutely had to block sebum at all costs"—finally paid off.

Wash durability is one of the metrics clients value most. According to the company, performance exceeding 30 washes is generally considered a benchmark for "durable water repellency," with many products claiming durability up to 50 washes. However, "dewelry®0" maintains a Level 4 water repellency rating even after 100 washes. This rivals the performance of fluorine-based water repellents (C8 type) that were once the industry standard—a target set right from the beginning of development.

"Very few companies can achieve 100-wash durability, so when we explain this at trade shows, even industry insiders are surprised and ask, 'Is that really true?'" says Asakura.

Going Beyond Spec Sheets: A Focus on Water Drop Roll-Off and Fabric Texture

Without sebum present, the contact angle of "dewelry®0" reaches approximately 160°. This significantly exceeds the roughly 110° of standard water-repellent fabrics, placing it squarely in the realm of superhydrophobicity. However, what Kogure pursued wasn't just numbers on a spec sheet. "We didn't focus too much on the contact angle figure itself. What mattered to us was how water droplets roll across the fabric's surface."

Comparing the sliding angle—the angle at which a tilted fabric allows a water droplet to start rolling—standard water-repellent fabrics require a tilt of 20° to 30° or more, whereas "dewelry®0" begins rolling at around 10°. Because water droplets don't remain on the fabric, situations where it feels wet are rare to begin with. The 160° contact angle was merely a byproduct of pursuing maximum roll-off ease.

Another challenge is that pushing solely for performance often makes the fabric stiff. In the early stages of development, non-fluorine processed fabrics were so stiff that folding them in half created sharp edges, but "dewelry®0" retains the fabric's original supple texture.

The strictest evaluation standards actually came from within the company; even if water repellency was high, if the texture wasn't good, the sales department would give it an immediate "NG." Achieving both durability and a soft texture was an absolute requirement right from the start of development.

Currently, the sports sector is where "dewelry®0" is most widely used. In mountaineering underwear, applying this treatment to the inner mesh fabric allows sweat to escape through the mesh holes to the outer absorbent layer, helping reduce sweat-induced chills. Because base layers remain in direct contact with the skin, the sebum resistance of "dewelry®0" truly shines. Future plans include expanding into outdoor gear such as down jackets.

Asakura describes "dewelry®0" as "still under development." It has become resistant to light contact with sebum, but the next target is repelling everyday oils, such as food spills and machine oil. "Chemical manufacturers don't make chemicals just for us. That's why we want to continue leveraging our processing innovations and expertise to create unique value."

Rather than relying on the chemical agent itself to repel oil, Asakura Senpu minimizes the impact of sebum through clever processing techniques. Delivering 100-wash water repellency, effortless water drop roll-off, and a soft texture all at once, "dewelry®0" continues to evolve. As they tackle the next challenge of repelling food spills and machine oil, Asakura Senpu is pushing the boundaries of non-fluorine water repellency through advanced processing technology.