Shock of up to -15°C! Beat the Japanese Summer Heat with the Ultra-Cooling "COVEROSS®" T-Shirt

In recent years, Japanese summers have grown dangerously hot, demanding ever more attention.

Many apparel brands have released cool-feeling T-shirts that emphasize breathability. But among them, the COVEROSS® "Ultra Freezer T-shirt" stands out for its next-level cooling performance.

Amazingly, the unique fabric and processing technology deliver a "cooling sensation" of up to -15°C.

This ultra-cooling Tee set record sales for T-shirts on Makuake in 2023, taking the fashion industry by storm. How was this innovative T-shirt born?

Moto Suzuki of Hap Inc. shares the full story—from development secrets to the logic behind the features.

The Goal: A T-shirt that Conquers Japan’s Extremely Hot Summers

The Ultra Freezer T-shirt was born to tackle the challenge of Japan’s extreme summer heat.

"With the heatwaves growing harsher every year, our customers told us, 'Regular cool-touch T-shirts just aren’t enough' and 'We want T-shirts that feel even cooler.'

What people need today is a T-shirt that 'instantly feels refreshing the moment you put it on—and stays comfortable even when you sweat.' So, we assembled a dedicated development team to answer those demands."

After years of research, the team developed the innovative "Ultra Freezer Technology," which combines a special cooling material with the proprietary COVEROSS® post-finish process.

"The T-shirt uses a special material—premium cotton on the outside and nylon on the inside. The cotton offers excellent breathability and moisture absorption, feels soft against the skin, and its natural look is a major appeal.

Meanwhile, the nylon uses a distinctive hollow fiber, infused with jade and ceramic to further boost cooling effects."

The addition of polyurethane gives the fabric superb stretch.

"At 17% blend, it’s several times higher than typical stretch T-shirts. This not only makes movement easier, but also enhances durability in washing and keeps its shape better. Above all, the improved fit lets you feel the cooling effect more effectively."

A Breakthrough Post-Processing Technology: Over 10 Features in One Fabric

But what is the COVEROSS® finishing featured in the brand name?

"It’s a post-processing technology that grants over ten functions to a single piece of fabric.

For example: cooling sensation, quick-drying, heat-shielding, UV protection, antibacterial/odor control, deodorization, antiviral, water repellency, pollen, mold and mite resistance, insect repellency, pilling prevention, moisture retention, heat-generating moisture absorption, far infrared, and color-fade resistance.

What’s special is that all these features can be applied evenly and gently, so the fabric quality isn’t compromised."

How can so many functions be applied to just one fabric?

"We use different agents for each function and fix them evenly onto the material. To make the features work without interfering with each other, we adjust the order and concentration of each treatment."

COVEROSS® T-shirts use a proprietary method that lets these agents penetrate and set deeply within the fibers—making the features highly durable and resistant to washing over time.

"This processing technology was jointly developed with our partner factory in 2016 and has since been continually refined. When applying it to T-shirts, selecting the right yarn, knitting technique, processing timing, and ensuring wash durability were some of the main challenges.

In particular, achieving cooling sensation, stretchability, and a pleasant feel on the skin at a high level, all at once, with a combination of natural and synthetic fibers, was an extremely difficult task. Our development team gradually achieved satisfactory results through repeated trial and error and experimentation."

In short, it's thanks to the cotton × nylon cooling fabric and COVEROSS® technology that this T-shirt maximizes both cooling effect and functionality.

"The special treatment allows sweat on the skin to be quickly absorbed and makes it easier for heat to be taken away through the heat of vaporization. This is why you feel cool even when sitting still, and you can feel the effect even more clearly when you sweat."

"-15°C" is certainly an impressive figure.

"When we say -15°C, we’re referring to the maximum perceived difference based on Q-max values indicating contact cooling performance, as well as the temperature difference between the inside of the T-shirt and the outside air.

In fact, in our in-house thermography and skin-surface temperature measurements, we confirmed a temperature difference of up to about 15°C compared to regular cotton T-shirts.

However, since precise measurements vary according to environmental conditions—such as temperature, humidity, and the amount the wearer sweats—we describe this as a cooling sensation equivalent to up to -15°C."

The duration of the cooling sensation and how the effect changes outdoors in intense heat or indoors are also points of interest.

"Since the structure promotes evaporative cooling when you sweat, the cooling feel lasts for a fair amount of time. In intense sunlight, heat-shielding properties help reduce the increase in perceived body temperature.

Indoors, the duration of the cooling effect may vary somewhat based on airflow and humidity, but besides contact cooling, the wear remains dry and comfortable so comfort is rarely compromised.

However, when temperatures rise above 35°C or in very humid conditions, the physical cooling effect diminishes."

The texture is smooth, breathable, and feels cool to the touch. There’s plenty of stretch for freedom of movement, making it ideal for sportswear. Since the surface is cotton, it looks natural and should fit a wide range of settings.

The silhouette is slightly relaxed.

"While keeping current fashion trends in mind, we carefully balanced the design so it looks stylish even when worn alone. It comes in four unisex sizes from S to XL."

Another plus is that the fabric is densely knit, making it less see-through.

"To ensure even white T-shirts aren’t see-through, we paid close attention to the thickness of the yarn and the knitting structure. Our focus was preserving the classic T-shirt thickness while keeping the overall look light."

Comfort has also been pursued in the details.

"The neckline uses sturdy binding, but without feeling tight. For the tag, we chose a heat-pressed printed label that won’t irritate the skin."

Achieved All-Time No.1 Sales Record in Makuake’s T-Shirt Category

The exceptional quality speaks for itself in the sales numbers.

"We launched on Makuake on July 2, 2023. Until then, no T-shirt had ever raised more than 10 million yen in support purchases alone. Remarkably, this T-shirt achieved 10 million yen in just five hours on the first day, reaching a total of over 22 million yen by the end of the 24-day campaign. This is the all-time top sales record in the T-shirt category (as of June 2025)."

That same year, the entire COVEROSS® technology received the "第11回技術経営・イノベーション大賞内閣総理大臣賞". This was in recognition of how COVEROSS® delivers both sustainability and high functionality in clothing, contributing to a circular society and the realization of wellbeing.

It’s also attracted plenty of attention from the fashion industry—a collaboration with "doublet (ダブレット)", designed by Masayuki Ino, came to life for the Spring/Summer 2024 Paris Men’s Collection. On the runway, T-shirts printed with "COVEROSS® is Cooling" were revealed.

Suzuki says he’s received delighted feedback from all over Japan.

"One customer said, 'It feels just like wearing air conditioning,' which left a big impression on me. I also received a heartwarming message: 'I gave it to my dad who works outside, and he’s so happy he wears it every day.'"

From here on, COVEROSS® aims to create "clothing that protects lives."

"We are actively developing wearables to combat heatstroke.

Rather than simply providing a 'cool feeling,' we want to deliver apparel that scientifically combines diverse functionalities and benefits people in a wide range of environments, from sports to construction sites."

The "Ultra Freezer T-shirt" is poised to become essential for tackling the intensifying summer heat, now a significant threat to daily life. We highly encourage you to experience the sensation of "wearing air conditioning" for yourself.