TEXTILES.ORG
The textile-heated garment industry is revolutionizing how we stay warm. Advanced Functional Fabrics of America (AFFOA), the organization I work for, is at the forefront of developments in the types of heat sources used, particularly how they are controlled for optimal comfort and efficiency.
Disposable hand warmers, popular for their immediate heat via the exothermic oxidation of iron, have reached a market size of $1.5 billion as of 2024, according to Cognitive Market Research. Although effective at generating heat, these warmers offer no control over heat output, which limits their lifespan and applications. Alternatively, phase change materials, which switch states (such as from liquid to solid) at predetermined temperatures to absorb or release heat, provide a significantly longer operational life. However, like chemical reactions, this physical process is challenging to control precisely.
Our research and testing at AFFOA show that electrical heating offers a significant advance in heat control within textiles. This method incorporates conductive materials such as carbon fiber or metal wires, which activate with electric currents and allow for adjustable heat settings. These elements vary, from traditional metal wires and carbon fibers to innovative solutions such as metalized yarns, conductive threads, printed inks and nanomaterials. Regardless of the material, all are governed by similar principles of thermal control.
On and off
Currently, the simplest thermal control in textiles involves switching the electrical source on or off, typically providing basic settings such as low or high heat. More sophisticated systems, including AFFOA’s Closed Loop Heating controller, now feature adjustable temperature control, akin to a residential thermostat. These systems predominantly use proportional-integral-derivative (PID) controllers that compute an “error” value based on the difference between a desired temperature set point and the actual temperature. The PID adjusts the power to the heating elements to correct this error, optimizing both comfort and energy use.
Into the future
Looking ahead, we at AFFOA see that in the future, thermal controllers in textiles are set to overcome the limitations of current technologies by integrating more advanced sensing and control mechanisms. Prospective systems might include distributed or infrared (IR) temperature sensors for a more precise monitoring of body temperature, or they might use indirect measures such as assessing the performance of the heater itself.
Additionally, future thermal management systems will likely account for variables such as user behavior, wear duration and battery status. These considerations will enable dynamic adjustments to heat output, moving beyond fixed temperature settings to accommodate real-time needs and preferences.
Extreme cold—a use case
Recent efforts are addressing the problem of protecting warfighters in extreme cold. There is a renewed arctic focus, with competition from near-peer adversaries venturing into colder climates. This increases the risk of cold-weather injuries, particularly frostbite, immersion injury and hypothermia. Another related issue is the loss of dexterity, particularly in the thumb and trigger fingers, which is critical to operating cold-weather missions.
Testing and gathering feedback through limited soldier evaluations of the heated arm sleeve in Alaska yielded actionable design improvements, including:
• A novel arctic-ready textile heating platform that can be used in multiple form factors and applications
• A library of cold-weather materials, including high-performance insulation fabrics and active heaters for arctic-use cases
• A manufacturing-ready design with a domestic supply chain that has been identified and tested
Individualized and smarter
As thermal control technology evolves, integrating sophisticated sensors and adaptive control systems in textile garments promises enhanced thermal comfort and improved energy efficiency. This progression points toward a future where textile heating is not only smarter but is more attuned to the wearer’s requirements and environmental conditions.
Effort sponsored by the U.S. government under Other Transaction Agreement number HQ00342390025 between Advanced Functional Fabrics of America Inc. and the government. The U.S. government is authorized to reproduce and distribute reprints for governmental purposes notwithstanding any copyright notation thereon.
The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the U.S. government. Use, duplication, or disclosure is subject to the restrictions as stated in Agreement HQ00342390025 between Advanced Functional Fabrics of America Inc. and the government.
Edin Insanic, Ph.D., is the principal system architect at the Advanced Functional Fabrics of America (AFFOA).
SIDEBAR: Improvements in wearable technology
by Marie O’Mahony, Ph.D.
Thermal control is one of the basic functions of textiles for apparel. Because it affords comfort, it can be tempting not to properly prioritize it, given textiles’ other performance factors. However, it’s useful to take note of the new hybrid fiber and fabric technologies that are offering improvements in wearable technology.
Outlast’s phase change material (PCM) was “developed for outer space, tried and tested on Earth,” the company boasts, and they are correct. The thermo-technology was originally developed by NASA for use in spacesuits to help protect astronauts from extreme temperature fluctuations in space. It was one of the success stories of NASA’s Spinoff program, offering technologies to subject matter experts for terrestrial benefits.
The microencapsulation of the PCM offered a unique approach to thermal regulation, with another point of difference that the fabric immediately felt different—actually cool to the touch. This, not surprisingly, quickly created the expectation of progress, and Outlast today has more than 100 patents, with applications that go beyond clothing to include bedding and other products.
Aerogel advancements
Researchers at Institut für Textiltechnik, RWTH Aachen, are working with aerogel, developing fibers that are made with 100% aerogel in a way that is scalable for manufacture and cost-effective. Cellulose aerogel textiles are offered as sustainable, as well as more flexible and with better draping qualities than more conventional aerogel products, which can suffer from brittleness.
The quality of these new fibers makes it possible to process them using conventional textile machinery. The ITA Group International Centre for Sustainable Textiles is an internationally oriented research and training provider with the Institut für Textiltechnik as its core.
Outlast is also working with aerogel to make its AERSULATE® nonwovens, the company’s latest development in thermoregulating textiles. The aerogel-based nonwovens are flame-retardant and remain functional under pressure and moisture. The product shows potential in the field of personal protective equipment and technical applications.
Unconventional wicking
In support of its belief that “the most sustainable solution is to use less and reuse more,” Freudenberg Performance Materials has launched Comfortemp® HO 80xR as a circular thermal insulation wadding. The materials are made using 70% recycled polyamide taken from end-of-life fishing nets, carpet flooring and industrial plastics that would otherwise end up in landfill sites. The remaining 30% uses virgin fibers. As it has a comfortable, soft handle, the fabric can be used for apparel. Produced as roll goods, the tendency of wadding to clump is avoided, giving garments a longer use life before further recycling is needed.
Marie O’Mahony, Ph.D., is an industry consultant, author and academic based in London.