Blog Post

Understanding CLO Values

At Roast, we use CLO values as part of our survey and analysis processes to help determine things like the average comfortable temperature ranges for our building in various seasons, based on the types of clothes our building’s inhabitants wear.

Understanding CLO Values

Clothing is our first line of defense against the cold. How well our clothing protects from frigid temperatures depends on its CLO value – a measure of clothing’s thermal insulation. CLO values were developed in 1941 as an attempt to explain the insulation value of clothing, and are used to help guide us on appropriate attire for a given environment.

In this blog, we’ll look at an abbreviated CLO value chart and briefly discuss how clothing functions to help maintain thermal comfort in our daily lives. It’s essential to keep in mind that CLO values are only to be used as a guide since thermal comfort is the result of a multi-faceted equation of indoor environment and human activity. Dressing with the “right” CLO values in mind doesn’t guarantee comfort or warmth, but it’s a great start! In a complete Roast survey, CLO values are just one of many pieces of information we consider when analyzing the results provided by your building’s inhabitants.

What Are CLO Values?

CLO is a value that describes the degree of insulation provided by an article of clothing.¹ A CLO value of 1 is equal to the amount of clothing required by a resting human to maintain thermal comfort at a room temperature of 21 degrees Celsius, or 71 degrees Fahrenheit.² Average indoor air temperatures in the US range from 68.5 to 75 degrees Fahrenheit in the winter, and 75 to 80.5 degrees Fahrenheit in the summer.³

A value of 1 CLO is based on a typical business suit, which includes a shirt, undershirt, trousers, and suit jacket. Traditional business suits are less commonly worn compared to when CLO values were created, but we can still use CLO values as a guide to what makes a thermally sufficient outfit, given a local temperature. The higher the CLO value, the more insulating value is provided by the clothing in question. The CBE Comfort Tool is an excellent resource for further exploring the relationships between CLO values, temperature, and human comfort.

Clo Value Example Chart⁴

Making Sense of CLO Values in the Real World

Here at Roast, we used our survey tool to track the summer CLO values in our office to determine if there were changes we could make to improve employee comfort and building efficiency. We average around .41 CLO, which is a long way from the CLO value of 1 for traditional office apparel. Using the CBE tool, we determined that we can keep our summer office temperature 5-8 degrees warmer than the usual target temperatures that assume a 1 CLO value. By reducing our air conditioning load, we saw fairly significant energy and carbon savings, and a much more comfortable workplace for everyone.

Since we’re always trying to improve employee satisfaction and productivity, we conducted a deep dive into the dataset generated over several Roast summers to understand the relationship between CLO values, comfort, and productivity. Essentially, we wanted to determine how often there was a mismatch between reported CLO value and a calculated ideal CLO value to be based on the temperature readings corresponding to past survey responses. The results were fascinating, showing occupants regularly, approximately 30% of the time, under or overdressed relative to thermal conditions despite a steady office temperature, and as a result, reported higher than necessary levels of discomfort. Perhaps most remarkable, they would both over and underdress in the same week. As a result of this analysis, we’ve reminded employees that we have a flexible office dress policy and encourage them to take advantage.

If your Roast survey shows your building’s employees wear clothing with CLO values that aren’t typical for your average indoor temperature range, recommendations about attire could help improve comfort. As the seasons change, you can reference CLO values to adjust the dress code in the office. Additionally, assessing CLO values could reveal bigger issues with your building’s heating, cooling, or ventilation needs. Trends of people dressing a certain way could be a direct response to an environmental condition, such as a particularly drafty window or an ineffective air vent.

Some of the variables that affect CLO values are posture and activity.⁵ If clothing is squeezed tight, such as by backpack straps, insulation will be weaker in those places. Sitting or lying down changes thermal insulation levels due to the compression of air layers in the clothing. However, depending on materials, chairs and other furniture can provide considerable insulation as well. Take a chair covered in fabric as an example. A sitting person’s clothing insulation value increases by up to .15 CLO, depending on the contact area between their body and the chair.⁶

While it’s possible to determine the increase in insulation provided by chairs, sleeping and resting positions are difficult to evaluate unless the individual is completely immobile. Body motion decreases the insulation of a clothing ensemble by pumping air through clothing openings and causing air motion within the clothing, negatively impacting the estimated CLO value of a given article. For example, wearing gloves while riding a bike will not keep your hands as warm as if you were still. The movement of your hands inside the gloves forces warm air out while biking, reducing thermal insulation.

Beyond clothing choices, general posture, and activities, another factor in addressing comfort is humidity. Water is a better conductor of heat than air, so if your clothes become damp with sweat, rain, or immersion, water replaces some or all of the air between the fibers of your clothing, causing a thermal loss through conduction or evaporation – ideal if you’re trying to cool off, but not so much when you want to stay nice and warm!

Take Steps to Increase Comfort in the Workplace

Whether you’re planning a brand-new office layout, reorganizing your building, or simply want to give your employees a voice about their comfort so you can make positive changes, Roast can help. Analyze the CLO values of the people in your workplace, along with a wide variety of other environmental comfort factors to promote a more comfortable and productive workplace. Sign up today for a free Roast trial, or contact us to learn more about introducing the science of comfort into your workplace.

1. https://ashrae.iwrapper.com/ViewOnline/Standard_55-2017, ASHRAE, pg. 2, Definitions, Nov. 1, 2017
2. https://www.vivint.com/resources/article/best-home-room-temperature, Vivint SmartHome, May 2019
3. https://www.cdc.gov/niosh/topics/indoorenv/temperature.html Indoor Environmental Quality, CDC, Sept. 1, 2015
4. ANSI/ASHRAE Standard 55-2010, Standard Thermal Environmental Conditions for Human Occupancy, ANSI.org, pg.21 Table B2
5. ANSI/ASHRAE Standard 55-2010, Standard Thermal Environmental Conditions for Human Occupancy, ANSI.org, pg. 19, Nov. 1, 2017
6. Textiles and Human Thermophysiological Comfort in the Indoor Environment, Radostina A. Angelova, pg. 44, Section 4.3.1, CRC Press 2016