Specialty Fabrics Review August 2024 - 74

[ MARKETS ] ADVANCED TEXTILES
Thermal control in
wearable technology
Textiles for heating and cooling sources
by Edin Insanic, Ph.D.
T
HE 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
74 SPECIALTY FABRICS REVIEW / August 2024
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 nearpeer
adversaries venturing into colder
climates. This increases the risk of coldweather
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.
 Continued on page 76
Specialty Fabrics Review August 2024

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