The +5℃ Warmth Effect: The Functional Material "Heat Navi" Used in "Move Sport" Wear

In recent years, the evolution of functional materials has been remarkable—something unimaginable in an era when one could only choose clothing made from natural materials sourced from plants and animals. This season, particularly noteworthy at "Move Sport" is "Heat Navi Ⓡ)" which warms up by converting light into heat.
 
To learn more about the functional material "Heat Navi," I visited Descente Japan Ltd. I spoke with Naoto Tominaga from the Research and Development Department, and Yuhei Nagamatsu from the Move Sport Marketing Department, who discussed popular products like the Soft Shell Hoodie.

Equipped with Unique Technology that Efficiently Absorbs All Wavelengths of Light and Converts it to Heat

While a rainbow in the sky is described as having seven colors, it is well-known that there are invisible infrared and ultraviolet rays beyond the visible spectrum from red to violet. All these different wavelengths of light generate some heat when they hit a material.
 
"Normally, while you may feel warmth in places exposed to strong direct sunlight, if you avoid the sunlight, they quickly cool down. Most materials, including skin and fabric, cannot absorb light and convert it to heat. Our functional material 'Heat Navi' has made this possible."

So explains Naoto Tominaga, who is involved in basic research and material development at the company. It is somewhat known that infrared rays are warm, but near-infrared, visible light, and ultraviolet also generate heat when they contact materials. "Heat Navi" efficiently converts sunlight into heat, warming the interior of clothing, and it is adopted in many Descente products.
 
"Among these, one of the most popular is the Soft Shell Hoodie from 'Move Sport,' worn by volleyball player Yuki Ishikawa (as shown in the top image of this article). It incorporates 'Heat Navi', is light and warm when worn, provides 2-way stretch for easy movement, and is also water-repellent. This combination of high functionality and an active image has contributed to its strong sales."

So says Yuhei Nagamatsu from the Move Sport Marketing Department. What is the underlying mechanism that makes "Heat Navi" feel warm when worn? I asked Tominaga.

Incorporating "Carbon-based Inorganic Substances" into Fibers to Give Fabric the Function of Efficiently Converting Light to Heat

It is common knowledge that wearing white clothing in summer is cooler because it absorbs less heat from direct sunlight compared to wearing black. However, in winter, wearing black doesn’t usually produce a significant difference in warmth. In contrast, when wearing clothing with "Heat Navi" that efficiently converts light to heat, the difference is quite obvious.

"The heat retention effect of +5℃ is recognized as a function of 'Heat Navi.' This is due to incorporating carbon-based inorganic substances into the chemical fiber threads used as the material. The challenge in development was to find a material with high efficiency in converting light to heat and to incorporate it into fibers.
 
"There are various types of carbon-based inorganic substances. While the specific material name is a company secret, it is quite challenging to adequately incorporate it into the fibers; if the composition ratio is too high, the fibers become weak, and if too low, the heat generation effect diminishes. Therefore, it is necessary to appropriately blend it for practical application in products. Depending on the wearing scenario and design, the place where it is incorporated varies among products, including the outer fabric, insulation, and lining," explains Tominaga.

"According to the diagram, the brightness level on a cloudy morning at 10 AM is said to be around 25,000 lux. Even at a darker level of 10,000 lux, there is a noticeable difference when comparing our conventional fabric with 'Heat Navi.' We confirmed a heat retention effect of +5℃ not only on sunny days but also on cloudy days."

Feel the Warmth with "Heat Navi" Products that Make Full Use of the "Three Principles of Heat Transfer!

"Heat transfer involves three phenomena: conduction, convection, and thermal radiation, which are collectively referred to as the 'three principles of heat transfer.' The 'Heat Navi' system utilizes carbon-based inorganic materials for heat radiation associated with light. It is often more efficient to convert light that penetrates not just the outer fabric but also the lining and batting into heat. Besides 'Move Sport,' several of our brands, including 'Descente' and 'Le Coq Sportif,' have adopted 'Heat Navi'" (Tominaga).

"The popular 'HEATNAVI TOUGH Softshell Hoodie' features a single-layer fabric, which makes it lightweight and easy to move in, while also being warm. Instead of separating the materials by the outer and inner fabric, the materials are divided by the surface and reverse threads, with 'Heat Navi' blended into the reverse thread" (Nagamatsu).

"The surface thread is visible on the outside of the garment, while the reverse thread is seen from the inside, so at first glance, it may appear like separate outer and inner layers. However, it is actually a single active layer. If you look closely from the inside, you can see a hint of the color of the surface thread" (Nagamatsu).
 
The single-layer softshell hoodie is an ideal item for those who love sports and fitness, suitable for wearing while active or casually. In contrast, the "HEATNAVI Nylon Full Zip Hoodie" is more appropriate as cold weather gear during waiting or travel than while being active, highlighting the differences in where the "Heat Navi" material is utilized.

"This hoodie uses nylon for the outer fabric and 'Heat Navi' mesh for the inner lining, allowing it to retain warmth more effectively. It can be adapted for everyday use as winter outerwear or worn during commutes to and from sports and fitness activities, or while spectating" (Nagamatsu).
 
Both options ensure you can comfortably endure the winter without looking bulky. It’s reassuring to experience a function that converts light to heat while wearing it subtly. We hope you try it on in-store and feel the +5℃ functionality for yourself.