We were looking for a new fabric because of issues with the pilling of the Pertex Quantum Air. This had not been a problem during my field tests, but many customers complained that the fabric was prone to pilling in various situations. We wanted to solve this issue so that our customers can wear UL Shirts comfortably on their hikes without worrying about pilling.

So I collected a variety of lightweight, highly breathable fabrics from various companies. It was, however, difficult to define the reason why pilling occurred. The problem was not always reproduced, and in fact, my own UL Shirt never had any pilling issues. Pilling was obviously triggered by the repeated friction with something hard and coarse over a long period of time but it was very difficult to confirm from actual field testing. Hence, I realized that a reproducible testing method was necessary to validate and compare fabric issues, using inspection machines and tabletop testing. I also needed to know and understand why and how the pilling occurred in the first place because Pertex Quantum Air, the original UL Shirt fabric, performed pretty well in the normal abrasion testing. Then, what other trial method might be appropriate? We discussed this with the professional inspection company.

Consequently, after repeated tests, we concluded that the structure of the ripstop was the cause of the pilling.

Because the ripstop yarn is stronger and thicker than other yarns, it is higher than other yarns, thus creating unevenness in the fabric. When ripstop yarns are rubbed against hard objects, the yarns are partially pulled out and pilling occurs. We recognized that this is a problem that can occur not only with Pertex Quantum Air but with all ripstop fabrics.

Therefore, we decided to collect plain weave fabrics that are flatter and less prone to pilling, and also made a prototype of a proprietary plain-woven fabric. However, the plain-woven and thin fabrics were not strong enough and did not have the texture that I was looking for.

Then I thought of Teijin’s Shadow Rip. To prevent the surface from becoming uneven, the ripstop yarns of the fabric are made of a high-strength fiber that has the same thickness as the other yarns. This structure prevents the ripstop part from snagging and causing pilling of the fabric. Moreover, the fabric is strong and durable.

This is the perfect one I was looking for, I thought at first. Only, the fabric was heavier than the Pertex Quantum Air we had been using, and it was slightly thicker and made of polyester instead of nylon. Since we are an Ultra Light gear manufacturer, I was not happy about the heavier weight of the fabric. We decided to make a prototype and test it to see how it would perform.

Various tests have already shown that the breathability is equivalent to Pertex Quantum Air, and also in field tests in the mountains, the prototype turned out to be equally comfortable to our existing UL Shirts made of Quantum Air. It offers high ventilation performance when the buttons are wide open, and it can be windproof at the core of the body when the buttons are closed. The sleeves can be easily rolled up, or the neck collar can be raised and buttoned up when cold. It was as useful as ever and performed well as hiking activewear. Furthermore, I was also able to discover new features, such as superior wrinkle-proof performance even after it is tightly tucked into a backpack.

Consequently, we decided to update the fabric to Shadow Rip based on the following new advantages: it feels as comfortable as the previous fabric, it is less likely to create pilling due to repeated rubbing which had been a problem in the past, and it does not wrinkle easily even when squeezed into a backpack.

Yet another problem, however, was discovered.

Compared with nylon, the polyester fabric turned out to be more prone to color transfers to something. Shadow Rip is not our proprietary fabric but is developed by Teijin, and has been used by other major outdoor manufacturers for some time.

According to Teijin, color transfer has never been an issue so far. So, it was only in our individual tests conducted at a testing agency that the color transfer occurred. We confirmed staining on white wool and silk fabrics when they were layered and adhered to dark-colored Shadow Rip fabrics. Each of us has a unique composition of perspiration, and the color transfer does not occur in everyone, but now that we know this might occur, we want to be open and share this information with all of you.

To be honest, I was reluctant to write something negative about an updated product in this Product Story. But after many trials and tests, we discovered the solution as described in the “Product Story 2” in the next section.

I feel that it is better than our previous product and ready to go out to the world. I look forward to hearing everyone’s thoughts on this newly updated UL Shirt. (March 2022)

Since 2022, we’ve transitioned the fabric of the UL Shirt from Pertex Quantum Air to Teijin’s Shadow Rip. While Pertex Quantum Air is made of 100% nylon, Shadow Rip is 100% polyester. At Yamatomichi, we’ve used nylon in many of our products, but this marks the first time we’ve adopted polyester as the main material for a clothing item. Though both are classified as synthetic fibers, nylon and polyester each have distinct characteristics. Through this change, we’ve come to truly understand the differences between the two.

Color fastness refers to how resistant dyed fabric is to fading or bleeding—essentially, how well the color holds up over time. It’s a key test to assess how easily a fabric changes color or transfers dye when exposed to elements like sweat, friction, or washing.

When production batches of Shadow Rip were completed, we conducted fabric testing as part of our quality control process. One result in the sweat fastness test stood out as concerning: in dark colors such as Black, Duck Green, and Terracotta, the test showed noticeable issues in two areas—how much the fabric’s color changed due to sweat, and how much dye transferred to other garments.

To investigate more thoroughly, we conducted an additional test using four types of fabrics—cotton, wool, polyester, and nylon—as dye transfer targets. The results showed clear dye transfer onto wool. Cotton and polyester were barely affected, while nylon showed minimal transfer, though not as significant as wool.

According to the JIS (Japanese Industrial Standards) protocol, the test involves soaking the dyed fabric in a sweat-like solution for 30 minutes, then pressing it against another fabric under 37°C for 4 hours. To better reflect outdoor use, we extended this contact time to 8 hours.

This extended test suggested that if dark-colored Shadow Rip fabric remains damp with sweat and rubs against light-colored or white wool fabrics for around 8 hours, dye transfer can occur.

In everyday casual wear, it’s unlikely for garments to stay wet for such a long duration. But in the mountains, it’s not uncommon to hike all day with a sweat-soaked back. That’s why it’s essential for us to confirm whether such issues could arise under the demanding conditions of outdoor use.

Ten testers logged 80 hours on the trails. To maximize efficiency, we created a special prototype nicknamed “Two-Face”—a single garment with different colors on each side.

To conduct a thorough evaluation, we recruited testers—primarily from our in-house team—and asked them to engage in long periods of intense, sweat-inducing activity. We decided to test not only the colors that showed issues in lab tests but also every planned color of Shadow Rip and every color of Yamatomichi Merino, including those that had passed inspections without concern.

To cover every possible combination, we created a detailed testing plan. Each tester wore a Merino 100% shirt in a specific color, layered with a UL Shirt made of Shadow Rip, and carried a backpack while hiking for several hours or running through the city to ensure they worked up a sweat. To improve efficiency, we also made a prototype known as the “Two-Face,” a single shirt with different Shadow Rip colors on the left and right sides.

In total, 10 testers participated in the trial. We tested 7 Shadow Rip colors and 9 Merino shirt colors, logging more than 80 hours of field testing.

As expected, we confirmed that dye transfer occurred when darker-colored Shadow Rip fabrics were layered over lighter Merino shirts, consistent with the results from the lab. In contrast, lighter Shadow Rip fabrics showed no signs of transfer, and darker Merino shirts did not display visible staining—even if slight dye transfer may have occurred beneath the surface.

Partway through this field testing process, a new question emerged. Based on past experience, we understood that sweat composition can vary depending on factors like body type, diet, and physical condition, which meant that sweat-induced fading or dye transfer was often inconsistent from person to person. However, during this round of testing, nearly every tester experienced dye transfer. This led us to wonder—was sweat really the main cause?

We revisited the color fastness test results and found that while the sweat fastness scores were the most concerning, the water fastness results weren’t ideal either. This suggested that sweat might not be the only factor. Instead, prolonged contact with moisture alone—regardless of whether it’s sweat or water—could cause dye transfer to white or light-colored fabrics.

In response, we decided to conduct a more rigorous round of color fastness testing. Fastness testing typically covers areas such as washing, sweat, water, and friction, and each manufacturer sets its own standards for passing grades. The test scale ranges from Grade 1 (poor) to Grade 5 (excellent), with half-step intervals such as 4–5, resulting in a 9-point grading system. In casual wear, a passing grade is often set at 3–4, and a score of 4 is generally considered acceptable. This seems to hold true in the outdoor industry as well. In fact, when we compared the results with polyester garments from other outdoor brands, we found that many also scored a 4 in both sweat and water fastness.

However, when we looked at the actual test fabrics with the naked eye, we saw that even with a passing score of 4, visible dye transfer onto white fabric could still occur.

Since this fabric is intended for use in shirts—items that sit close to the body and are likely to come into contact with damp base layers worn underneath—it’s especially important to consider the real-world implications. Our customers may wear any number of underlayers. So even if a fabric technically meets the standard with a score of 4, if there’s still a chance of visible dye transfer, we at Yamatomichi feel responsible for finding a solution.

Shadow Rip is a fabric made entirely from polyester. While Yamatomichi has long worked with nylon, our experience and data regarding polyester have been relatively limited. This prompted us to revisit and research the characteristics of polyester more deeply. In general, synthetic fibers like nylon and polyester are considered less prone to fading or dye transfer compared to natural fibers such as cotton and wool. However, the results of our recent field tests told a different story: nearly all testers experienced significant dye transfer, and it occurred far too easily.

Further research revealed some useful insights. While polyester is generally described as resistant to fading and dye transfer, it is also noted that exposure to moisture over long periods can increase the risk of bleeding. We also came across another key detail: during the fabric finishing process, a washing step is used to remove excess dye that hasn’t fully bonded to the fibers. However, if this residual dye isn’t completely eliminated, it can later leach out when the fabric becomes wet or is washed.

To test the hypothesis that dye transfer might be due to residual, unbound dye left over from production, we conducted additional color fastness tests on Shadow Rip fabrics in both their brand-new state and after several wash cycles. The results showed that fastness improved noticeably after repeated washing, suggesting that the excess dye was indeed being washed out over time.

We shared these findings with the fabric manufacturer, who explained that polyester has a tendency to release dye that was absorbed between fibers during heat-setting, regardless of how thoroughly it was cleaned during production. In the case of Shadow Rip, the finishing temperature was kept relatively low to preserve the fabric’s soft texture. However, under the demanding conditions of outdoor use—particularly when garments stay wet for extended periods—this can lead to dye transfer.

That said, the dye fastness of Shadow Rip still meets general apparel industry standards, and the manufacturer noted that no issues have been reported by other outdoor brands using similar polyester fabrics.

We also consulted with a testing agency, and their assessment aligned with ours: nylon is dyed through chemical bonding, while polyester absorbs dye into its fibers, resulting in weaker bonding strength. This makes polyester inherently more prone to fading and dye transfer compared to nylon.

On the positive side, we found that repeated washing significantly improved the color fastness of darker shades, bringing many of them up to Grade 4–5 or even Grade 5. This reinforced our belief that concerns over dye bleeding could be addressed through proper washing. However, the manufacturer informed us that washing the fabric multiple times during the production process is not realistic. As a result, we concluded that the most effective solution was to pre-wash finished products at the factory before selling them to customers.

With this approach, we moved forward with releasing our newly updated products featuring Shadow Rip. The entire process turned out to be a valuable learning experience that deepened our understanding of color fastness. It also reminded us that industry standards are only a guideline, and that we need to evaluate quality based on a combination of factors—product purpose, expected usage conditions, and our own design principles. This experience inspired us to create a dedicated page summarizing color fastness results for Yamatomichi products.

If we were to optimize purely for color fastness, it would inevitably limit our color choices. But at Yamatomichi, we believe that while function and utility take priority in design, color should be a place for creativity and freedom. Of course, we will continue to do everything we can to improve dye fastness, but in cases where the nature of the color or fabric carries a risk of dye transfer, we’ll be transparent and clearly communicate those possibilities in advance.