This page was printed from

Evolving heat

The current and future state of thermal controllers in heated garments.

Features | May 27, 2024 | By: Edin Insanic, Ph.D

Students in Cold-Weather Operations Course (CWOC) class 22-03 practice snowshoeing and pulling an ahkio sled with gear as a team in January 2022 at a training area on South Post at Fort McCoy, Wis. Photo: U.S. Army/Scott T. Sturkol. 

The textile-heated garment industry is revolutionizing how we stay warm. Advanced Functional Fabrics of America (AFFOA) is at the forefront of developments in the types of heat sources used, particularly how they are controlled for optimal comfort and efficiency. 

Heat sources in textiles

Disposable hand warmers, popular for their immediate heat via the exothermic oxidation of iron, have reached a market size of US$1.5 billion as of 2024*. 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 like metalized yarns, conductive threads, printed inks and nanomaterials. Regardless of the material, all are governed by similar principles of thermal control.

Thermal controllers

Currently, the simplest thermal control in textiles involves switching the electrical source on or off, typically providing basic settings like 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 setpoint and the actual temperature. The PID adjusts the power to the heating elements to correct this error, optimizing both comfort and energy use.

The future of thermal management

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 the warfighter in extreme cold. There is a renewed arctic focus with competition from near-peer adversaries venturing into colder climates. This shift 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.  

After thoroughly reviewing available state-of-the-art technologies and a deep dive into the latest research on cold weather biology, AFFOA, in collaboration with their Fabric Innovation Network (FIN) members, has created a solution by developing a powered forearm sleeve that maintains dexterity and reduces cold weather injuries. The Institute leveraged its knowledge of the domestic ecosystem to identify necessary technologies, and design and prototype forearm sleeves and gloves. The garment was integrated into an arctic-ready closed-loop heating system and specialized high-performance insulation stack.

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, the integration of sophisticated sensors and adaptive control systems in textile garments promises not only enhanced thermal comfort but also improved energy efficiency. This progression points towards a future where textile heating is not only smarter but is also more attuned to the wearer’s requirements and environmental conditions.

Edin Insanic, Ph.D, is Principal System Architect at the Advanced Functional Fabrics of America (AFFOA). 

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.”

Share this Story