Clo cover photo

Word of the Month: Clo

What is clo?

Clo is a unit of measurement used to describe the amount of thermal insulation provided by a clothing garment or outfit. Different garments have different clo values. One clo, equivalent to 0.155 m2·°C/W(0.88 ft2·h·°F/Btu), is the amount of thermal insulation in an outfit that will keep a person comfortable in a room at 70°F with normal ventilation. A clo value of 0 corresponds to a naked person.

An example

To better understand clo, we can break it down. Let’s look at a TherMOOstat comment from Aug. 21, 2017, in Valley Hall when 70°F:

“The entire building is freezing. I was wearing pants, a sweatshirt, and fuzzy boots and wished I had a blanket because it was so cold.”

This person's outfit can be broken down by clo values:

  • the pants would have 0.24 clo
  • the sweatshirt would have 0.34 clo
  • the boots would have 0.10 clo

This adds up to a clo value of 0.68, which helps to explain why the person feels cold. In this environment, where the temperature of the room is the standard 70°F, the person needs approximately 0.32 more clo in order to attain the standard clo value of 1 and feel comfortable. The person could, for example, put on a jacket, which has a clo value of 0.36, or a long-sleeve flannel, which has a clo value of 0.34.

Why clo is important?

Knowing how clo works can be remarkably helpful for various reasons. Unfortunately, campus buildings cannot be tailored to every individual’s particular temperature desires, because communal spaces are difficult for individual occupants to control. Further, standardizing a building's Heating, Ventilation, and Air Conditioning (HVAC) system for the majority is more economically and energy efficient than a system that is constantly adjusted via wars over the office thermostat. Understanding clo helps us adapt to these circumstances. Wearing layers depending on your desired comfort level will adjust the clo of your outfit and keep you comfortable in classrooms and offices on campus.

How much clo is Joules wearing?

joules Clo

In the first square, Joules’ sleeveless vest is only 0.22 clo. She’ll need to put on quite a few more layers to be comfortable. In square 2, Joules adds on a fancy suit jacket, worth 0.44 clo. Now at a clo value of 0.66, she’ll be more comfortable than she was in the vest, but she won’t quite be at an adequate level of clo. Once Joules adds to her outfit boots, worth 0.10 clo, and a long-sleeve, worth 0.25 clo, her total outfit will be 1.01 clo. She will now be comfortable in a room at 70°F.


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