Why "12% Cashmere"? The Golden Ratio of Warmth and Strength Engineered by PLST and Toray

For ages, winter fashion has forced a choice between warmth and style. Layering up meant looking bulky, while prioritizing a sleek silhouette meant shivering in the cold. The blurry line between innerwear and a top was a particular headache for many women, who dreaded their functional base layers peeking out or the itchy feel of a knit sweater.

The 'Warm Reserve Cashmere Blend' from PLST Co., Ltd., launched for the Winter 2025 season, is a definitive solution to this problem. Infused with cashmere and engineered with moisture-wicking, heat-generating, insulating, and stretch properties, it functions like innerwear but is designed as a standalone 'T-shirt,' completely redefining the boundaries of your winter wardrobe.

In this article, we sit down with Gentaro Saito, the head of product development at PLST, to explore the development process with Toray Industries, Inc. and uncover the data-driven logic behind the fabric’s design.

Proximity to Toray: The Secret to Rapid Development

The key to developing the 'Warm Reserve Cashmere Blend' was the team’s close physical proximity to its strategic partner, Toray Industries, Inc.

Toray representatives are stationed full-time at the Fast Retailing Group offices—home to PLST, Uniqlo, and GU—giving the development team an environment for daily, face-to-face discussions.

Saito explains how this unique setup impacts the development process.

“Whenever we had a new idea or hit a roadblock during product development, we could just walk over to the Toray team and have a direct conversation about the materials. That’s exactly what happened with the 'Warm Reserve Cashmere Blend' development.”

The goal was to blend a polished, office-appropriate feel with everyday casual comfort. Achieving this required countless tiny adjustments and tests, and it was this intensely collaborative environment that made such a complex fabric design possible.

Typically, cashmere-blend products can range from items labeled 'cashmere blend' with as little as 5% to those that market their 100% purity.

So, why did they land on the precise figure of 12%? The answer lies in a complex trade-off between three key factors: physical properties (strength), cost, and performance (feel).

“The more cashmere you add, the softer and more comfortable the fabric becomes. But too much of it drives up the price and compromises its durability in the wash. We were looking for that perfect balance between a luxurious feel, the durability needed for everyday wear, and a price customers would find approachable. After countless prototypes, we landed on 12% as the magic number.”

Saito's explanation makes it clear that 12% wasn’t an arbitrary choice but a precise threshold identified after analyzing vast amounts of test data. This percentage allows the fabric to be machine-washable for easy care while delivering a luxurious feel from the moment you put it on. On top of that, it enables the team to stick to a strategic price point of under 5,000 yen.

That 12% was the single point where all these critical conditions intersected.

The Four-Fiber Weave: Engineering Warmth and Structure

The 'Warm Reserve Cashmere Blend' is not made of cashmere alone. It relies on a 'hybrid structure' where four different fibers—rayon, acrylic, cashmere, and polyurethane—each perform a distinct and vital role.

Saito breaks down the specific role each of the four fibers plays:

“To build three functions into one fabric—moisture-wicking heat generation, insulation, and stretch—we created a design that leverages the unique properties of each fiber.

First, rayon absorbs moisture and vapor from the body to generate heat. Then, acrylic traps that heat to provide insulation. We add cashmere for even more warmth and a smooth, luxurious feel. Finally, polyurethane provides the stretch that ensures a comfortable fit.”

By working together like a relay team, these four fibers allow a thin fabric to deliver impressive warmth. As Saito notes, “the material choice was all about leveraging the unique strengths of each fiber.” This wasn't a happy accident—it was a deliberately engineered system of functions.

The key to maximizing the material's functionality and creating a piece stylish enough to be worn on its own lies in the design and pattern. Saito was particularly passionate about blurring the line between innerwear and outerwear.

"This isn't just an undershirt by any means. I wanted to create something that doesn't scream 'innerwear' when peeking out from under a jacket, something you'd feel confident wearing even after taking the jacket off. To achieve that, the fit is absolutely key.

A skin-tight fit would be too revealing, while a baggy one would look bulky. We designed it with a straight silhouette and a relaxed fit that elegantly skims the body without clinging."

From a functional perspective, this "skimming the body" fit means creating just the right amount of "clearance" or space between you and the fabric. This space brings two significant benefits.

The first is better insulation. A layer of air trapped between the fabric and your skin acts as a natural insulator, adding to the material's own heat-retaining capabilities. This creates a barrier against the cold, helping to keep your body temperature stable.

The other benefit is a figure-flattering effect. Because the fabric doesn't cling to your skin, it smooths over your silhouette without emphasizing lines around the back and sides, creating a slimming visual effect. This smart design is why Saito is so confident that it "looks chic even on its own."

The sleeve design is another example of functional beauty at its best.

"We designed the sleeves to be a bit longer and incorporated elastic shirring. This ensures they fully cover your wrists, providing extra warmth. It also allows them to be fashionably bunched up or peek out from under a jacket or sweater cuff, adding a nice accent to your look. With typical innerwear, you'd hide the sleeves, but by designing them to be seen, we've elevated the top into a polished standalone piece."

Your wrists are where blood vessels run close to the skin, so keeping them warm is a highly effective way to raise your perceived body temperature. The fact that a single detail—shirring—solves both the functional need for warmth and the stylistic desire for a layered accent is a testament to PLST's signature practical approach.

Aiming for 'LifeWear' That Enriches Your Life

This series comes packaged in a special gift box, designed not just for you to treat yourself, but also to meet the growing demand for thoughtful gifts.

"We've heard from so many customers who wanted to give PLST items as gifts. At under 5,000 yen, the price is approachable, and the high-quality box adds a sense of occasion. We really focused on creating packaging that makes you want to share it with someone."

Saito concludes by sharing the ultimate vision for the series:

"This is a premium piece that delivers on both style and warmth—the kind of top you’ll want to wear daily. It’s not about dressing up for a special occasion. Instead, as we strive to create ‘LifeWear’ that truly enriches the everyday, we hope this piece will be discovered and loved by many people."

Born from a powerful partnership with Toray and meticulous material engineering, the "Warm Reserve Cashmere Blend" is poised to become the new winter staple for modern women who refuse to choose between function and style.