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Development Story of Our Silk Circular Rib Knit Fabric

MUUGI’s 100% Silk Circular Rib Knit Series is made from an original fabric developed with meticulous attention to the yarn. Creating fabric from scratch is a somewhat rare case not only for underwear brands but also in the fashion industry. Through repeated trials and errors, we developed this fabric aiming to create the perfect base for ideal underwear. On this page, we will introduce this original fabric in detail.

Clothing is broadly classified into three categories:

  • Woven fabrics
  • Cut-and-sew (circular knit)
  • Knitwear (flat knit)

MUUGI’s Silk Circular Rib Knit Series falls into the cut-and-sew category. Cut-and-sew refers to clothing made by knitting yarn into circular knit fabric, then cutting and sewing it.

Generally, when fashion brands create cut-and-sew garments, they often select fabrics available in the market. The benefits of this approach include faster development speeds and lower development costs since there is no need for trial and research. Additionally, because these fabrics are produced in bulk, the production costs can be relatively lower.

However, at MUUGI, we chose to create our own original fabric instead of selecting from available market options. This decision was driven by the fact that the perfect fabric for what we wanted to create simply did not exist. 100% silk fabric is generally expensive and not commonly purchased by typical apparel manufacturers, making it less available in the market. Moreover, the specific qualities we desired—easy to wash at home, smooth and comfortable to the touch, with just the right amount of stretch, and neither too thick nor too thin—were very niche. When we discussed this with the president of a fabric factory, he told us, "Such a fabric doesn't exist in the market," leading us to start from scratch in creating our original fabric.

Creating fabric is a collaborative effort with professional fabric factories. We were fortunate to partner with a factory skilled in working with silk and ultra-fine yarns, which are particularly challenging to knit. Together, we embarked on the journey of co-developing our fabric.

There are many variables involved in fabric production, such as the type of yarn, yarn count (thickness), knitting method, and gauge (stitch density). The combination of these factors results in different fabric characteristics. Here, we will explain the yarn count, knitting method, and stitch density in detail.

First, let's talk about the yarn count. Even with 100% silk yarn, there are various "counts" available. The "count" is a measure related to the thickness of the yarn, generally indicating that the higher the number, the finer the yarn. (The world of yarn count can be quite complex, so we'll skip the detailed explanation here.) In simple terms, for cotton yarn count, yarns with a count below 20 are considered "thick count," resulting in a thick and sturdy texture. Yarns with a count between 30 and 50 are "medium count," commonly used for general T-shirts. Yarns with a count above 60 are "fine count," known for producing fabrics with a sheen and smooth texture. Additionally, yarns with a count over 100 are referred to as "superfine count."

Next, let's discuss the knitting method. Circular knit fabrics used in cut-and-sew garments include various knitting methods such as "jersey," "circular rib knit," and "pique." For example, most common T-shirts are made with "jersey knit." Even with the same yarn, the knitting method can significantly affect the fabric's stretch, thickness, and smoothness.

Lastly, let's examine "stitch density." Generally, a higher density, known as "tight density," results in a firm and structured texture, while a lower density, known as "loose density," produces a relaxed and soft texture. This setting significantly affects the fabric's feel, quality, elastic recovery (ability to return to its original shape), and elasticity.

Now, let's return to the story of co-developing MUUGI's original fabric.

When we explained the product concept and the requirements for the ideal fabric to the fabric factory, they suggested using either 120-count or 240-count yarn. We immediately procured these two types of yarn and began prototyping. These counts are among the finest and most delicate in the world of yarn. Particularly, 240-count silk is extremely rare and challenging to handle, with very few factories capable of working with it. The finer the yarn, the more waste is produced, lowering productivity, and handling such yarn requires a high level of skill (the factory we collaborated with is known as a go-to place for handling 240-count silk).

Next, as candidates for the knitting method, we considered not only the common "jersey knit" but also "circular rib knit," which offers high lateral stretch. We also explored suitable settings for the stitch density as we continued the development.

After prototyping several fabrics and creating samples of the underwear with built-in bra, we conducted fitting tests. As a result, we ultimately decided to use 240-count circular rib knit fabric with the tightest stitch density.

Regarding the yarn, the 120-count produced a fabric with a substantial thickness and a soft, plush feel, while the 240-count resulted in a smooth and delicate texture, both of which were excellent. However, the underwear with built-in bra that we initially wanted to create at MUUGI had a structure with three layers at the front and two layers at the back. The 120-count fabric was too thick, making it uncomfortably warm. On the other hand, the 240-count fabric provided a unique, delicate texture that we found to be one-of-a-kind. Therefore, we decided to use the 240-count yarn.

As for the knitting method, we decided to adopt the "circular rib knit" because of its significant characteristic of high lateral stretch, which provides a snug fit to the body. The fabric's ability to gently conform to the body's movements, especially during breathing, felt truly comfortable.

Regarding the stitch density, we concluded that using the extremely fine 240-count yarn with the highest possible stitch density would be optimal for underwear, providing both a delicate feel and a sense of firmness.

The extremely fine 240-count yarn tends to result in a flimsy, loose fabric with weak elastic recovery (kickback) due to its thinness. Such a loose fabric would fail to provide the desired snug fit around the bust area. However, by maximizing the stitch density, we balanced the fineness of the yarn with a fabric that is both soft and firm, achieving the perfect feel for our underwear.

Even when stretched horizontally, the fabric maintains a tightly packed density, and its gentle elasticity ensures a comfortable, snug fit. Once you wear it, you will experience the exceptional quality of MUUGI's original silk fabric.

Knitting rib fabric with ultra-fine yarn at the highest possible density is extremely challenging and can only be achieved with the knowledge and skills of seasoned artisans. This complex production process involves many difficulties, but it results in a high-value product that is hard to find elsewhere. That's why we continue to cherish and produce this unique fabric.

We've discussed the background of our fabric creation: 100% silk, 240-count ultra-fine yarn, circular rib knit, and tight stitch density. These are aspects you can see, touch, and feel when you wear the fabric. Additionally, this fabric has elements that you will appreciate over long-term use.

This is where the "washable treatment" comes in.

Underwear is something you use every day, and since it gets dirty, you want to be able to wash it easily at home. Additionally, it needs to be made from fabric that lasts as long as possible, not something that falls apart quickly. From the very beginning, this was a non-negotiable requirement in our development process.

However, silk is inherently a very delicate material that is sensitive to water and friction. Washing it often results in a rough texture or a whitish appearance. This phenomenon is known in technical terms as "fibrillation." Silk fibers break down into fibrils, causing the surface to become coarse, lose its luster, appear whitish, and weaken, making it prone to tearing. We occasionally hear from customers, saying things like, "I bought silk underwear in the past, but it quickly became rough and unusable," or "After a few wears, the fabric tore." This is likely due to the fibrillation of the silk.

To prevent this fibrillation, we use "washable treatment" technology. In recent years, washable treatment technology for silk has advanced, and we've seen more products labeled as "washable silk." However, not all washable treatments are the same; they vary in methods and degrees. Washable treatments can be categorized into three main types based on when the treatment is applied.

The first type is applied to the "fabric" before it is cut. This is the most superficial treatment. The second type is applied to the "yarn" before it becomes fabric. Imagine the treatment coating the surface of the twisted yarn. The third type is applied to the "fiber" before it is spun into yarn. This involves the treatment penetrating deep into the fibers, providing thorough protection.

At MUUGI, we use the earliest stage treatment, applying the washable treatment to the fiber before it is spun into yarn. This method ensures greater durability against water and friction, and the treatment remains effective permanently, even after repeated washing. Our fabric retains its softness, color, and strength, preventing it from becoming rough, faded, or weak over time.

Regular silk (without washable treatment) after being wet and subjected to friction. The fibers have broken down and are damaged.

Silk treated with washable processing at the fiber stage after being wet and subjected to friction. The fibers show no damage.

Its durability goes beyond "hand-washable" to the point where you can machine wash it just like your regular clothes. (However, to maintain the best texture for as long as possible, we recommend using a neutral detergent and a gentle cycle. Also, please be sure to use a laundry net.) Even after prolonged use, the fabric retains its soft feel and rich color.
We hope you will enjoy the lasting comfort and durability of this fabric for many years to come.

Comparison after 30 machine washes. The left side shows regular silk (without washable treatment), and the right side shows silk treated with washable processing at the fiber stage. The untreated silk on the left has whitened, the fabric is damaged, and it has a rough texture. The treated silk on the right remains black without whitening, and its texture has not changed.

This concludes our story about MUUGI's silk circular rib knit fabric. In the latter part of this page, we have included an article about our visit to the factory where this fabric is made.
If you found this interesting, we hope you will take a look at the article as well.