Clo Values...What’s That?©

 

 

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 to leave a comment on either site.  I announce new articles on Facebook at Eric Reynolds, on Instagram at bandanamanaproductions, and on VK at Eric Reynolds, so watch for me.

 

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