Humans
originally come from the tropics and that is why we create artificial, tropical,
microclimates in our homes, offices, cars and beneath the layers of clothes we
wear. And everyone knows that clothes
keep you warm and protect you from the cold, but just how much protection do
they provide? That is the question that A.P.
Gagge, A.C. Burton, and H.C. Brazett wanted to answer in the early 1940s.
So,
they did the research, and in the November 7, 1941, edition of Science they published,
“A Practical System of Units for the Description of the
Heat Exchange of Man With His Environment” explaining what a “Clo Unit”,
a measurement value that they had created, was.
Gagge
et al., created the concept of the “Clo unit” to measure the thermal
resistance of clothing, which was called “clothing insulation”. They measured the insulation of clothing in “Clos”
which shows the clothing’s, not of fabric’s, ability to prevent the transfer the
body’s heat to the environment, and which considers the effect of air movement both
inside clothing through body movement, and of wind outside the clothing. A “Clo
unit” as a value of clothing insulation can be used to gauge the
effectiveness of clothing to maintain the body’s normal temperature and as an
insulating protection from the environment.
The
factors that affect thermal comfort are air temperature, wind speed
(convection), heat conduction from you to other objects, radiation from you or to
you from other objects or heat sources, humidity, activity, and clothing. Your clothing is the primary shelter
protecting you from the environment by controlling the heat transfer from your
body to the environment and vice versa.
The
enclosed air layer trapped between your skin surface and the first layer of
your clothing creates a microclimate that provides you, as a member of a tropical
species, with the warmth necessary for your survival. This microclimate is the air layer trapped nearest
to your skin. Although the factors
stated above need to be considered, the measurement of clothing insulation, in “Clo”,
offers a simple way to determine whether people feel comfortable in the
clothing that they are wearing.
So, how
warm are your clothes...
Your
clothes work as a unit, and they can be layered to increase or decrease
insulation you need. Clothing provides
insulation because of the low heat conduction of the air trapped within its
layers. The overall thickness of
clothing is responsible for its insulation value, since as layers increase more
areas of trapped air are created. An overall
thickness of 1 inch of clothing (2.5 cm) is considered to have an insulation
value of approximately 4.0 clo. However,
the amount of insulation that is provided by adding extra layers of clothes is
limited by the increasing restriction of movement caused by the bulk of the
extra clothes. In general, 1 inch to 1-½
inches (2.5 to 3.75 cm) has been accepted as the upper limit in thickness that
can be easily worn.
The
insulation, or clo value, of your clothing is decreased by moisture content trapped
within it. This is because wetting clothes
reduces their ability to trap air. The
greater the moisture content, the less the insulating value of the clothing,
and even a small amount of sweat will decrease the insulating value of your clothes. This is why layers should be removed as
activity increases or waterproof outer layers should be worn when wet weather conditions
are experienced.
Also,
when your clothes are compressed, either by wearing clothes that are too tight,
by over-layering, or by wearing a pack, their insulation value will be reduced due
to the compression of air layers trapped within them. Additionally, sitting or lying down will reduce
the clo value of your clothes.
Body
motion and activity also reduces the insulation value of your clothes by
pumping air through openings in your clothes and causing air movement within
your clothing. Wind also quickly diminishes
the insulation value of your clothes by blowing away the layers of warmed air
trapped inside your clothes, this is why a windproof/waterproof outer layer is
so vital to staying warm.
So,
that is how you know just how warm your clothes are and why layering and
staying “comfortably cold” works, and it is all thanks to the research
of A.P. Gagge, A.C. Burton, and H.C. Brazett and their “Clo unit”.
Don’t forget to come back next week and read “Burning Calories for
Heat ©”, where we will talk about how your body creates the heat that your
clothes trap close to your skin.
I
hope that you continue to enjoy The Woodsman’s Journal Online and look for me
on YouTube at BandanaMan Productions for other related videos, HERE. Don’t forget to follow me on both The
Woodsman’s Journal Online, HERE,
and subscribe to BandanaMan Productions on YouTube. If you have questions, as always, feel free
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announce new articles on Facebook at Eric Reynolds, on Instagram at
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That
is all for now, and as always, until next time, Happy Trails!
Sources
A.P.
Gagge, A.C. Burton, and H.C. Brazett; “A Practical System of Units for the Description
of the Heat Exchange of Man With His Environment”, Science, November 7 1941,
Vol 94, Issue 2445, page 428-430, https://www.science.org/doi/10.1126/science.94.2445.428,
accessed December 2, 2023
Auliciems, Andris; and Szokolay, Steven
V.; Thermal Comfort, https://www.researchgate.net/publication/234169993_THERMAL_COMFORT/link/0fcfd50fd28d99989b000000/download,
accessed December 2, 2023
Eisberg, Harry Belleville; Owens, J. E.; Fundamentals of Arctic and Cold Weather
Medicine and Dentistry, [U.S. Navy Department, Washington, DC, 1949], https://books.google.com/books?id=2-bYnbMCwYQC&pg=PA80&dq=clo+values&hl=en&newbks=1&newbks_redir=0&sa=X&ved=2ahUKEwjJtpavyMuCAxU0KlkFHWKIByYQ6AF6BAgFEAI#v=onepage&q=clo%20values&f=false
Kyunsoo, Lee; Haneul,
Choi; Hyungkeun, Kim; Daeung, Kim Danny; and Kim, Taeyeon; “Assessment of a
Real-Time Prediction Method for High Clothing Thermal Insulation Using a
Thermoregulation Model and an Infrared Camera”, Atmosphere 2020, Vol.
11, No. 1, page 106, https://www.mdpi.com/2073-4433/11/1/106,
accessed December 2, 2023
Lundgren,
Peter; Björnstig, Ulf; Kuklane, Kalev; “Protection Against Cold in Prehospital
Care -- Thermal Insulation, Properties of Blankets and Rescue Bags in Different
Wind Conditions”, https://www.researchgate.net/figure/Thermal-insulation-clo-for-insulation-ensembles-in-the-low-insulation-group-at-low_fig2_40909134,
accessed December 2, 2023
Roast; “Understanding CLO Values”,[© 2023 KT Innovations], https://roastsurvey.com/blog-post/understanding-clo-values/#:~:text=What%20Are%20CLO%20Values%3F,by%20an%20article%20of%20clothing.&text=A%20CLO%20value%20of%201,Celsius%2C%20or%2071%20degrees%20Fahrenheit,
accessed December 2, 2023
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