How clothing plays a role in the thermostat wars
A suit and a summer dress can differ by six degrees of comfort. What clo values are, why desert and arctic clothing look the way they do, and what it means for setting an office temperature.
The body is constantly generating heat and constantly needing to shed or conserve it. Clothing is the tool we invented to manage that, and it is the reason our species is not confined to a narrow band of the planet.
This is the next instalment in our series on thermal neutrality. Having covered metabolism, we turn to the variable people control most directly — and account for least.
Form follows function
Clothing designed for thermal management does one of two jobs: it speeds heat loss, or it slows it. Look at what different climates arrived at and the physics is written on the surface.
Hot, dry climates
Desert clothing is loose, porous, pale, and covers almost the whole body. Each of those is doing something specific.
Loose allows air to move in the gap between cloth and skin, which drives convective heat loss and evaporative cooling.
Porous lets humid air diffuse away from the skin. In non-porous cloth the air next to you saturates, evaporation stalls, and your main cooling mechanism stops working.
Covering reduces the skin area exposed to radiant gain. The body absorbs radiation extremely efficiently, which is a liability under a desert sun.
Pale because lighter surfaces absorb less. Cover up and stay light, and the sun heats your clothing rather than you.
Cold climates
Reverse every requirement. Winter clothing is thick, insulating, and closed at the openings.
Thickness and low conductivity slow the transfer from the inner layer to the outer. A modern snowsuit does this with a non-porous shell over a lofted down filling — down works because it traps a great deal of still air for very little weight, which is what replaced fur and wool coats.
Covering matters here for the same reason as in the desert, running the other way: exposed skin radiates heat away fast when the surroundings are cold. Sealed cuffs, ankles and collars stop convective loss through the gaps.
The advice to cover up in winter is not folklore. It is the largest heat-loss route being shut down.
What a clo is
A clo is the unit of thermal insulation for clothing. One clo equals 0.155 m²K/W, and represents roughly the insulation a seated person needs to be comfortable at 21 °C (70 °F) with humidity below 50%.
For reference, 1.0 clo is approximately a business suit. A light summer outfit is nearer 0.5 clo.
Clo values exist because comfort modelling needs a number for what people are wearing. Without one you cannot predict whether a room will be comfortable, since clothing shifts the answer more than most of the other variables.
And this is where the office argument comes from
The standard comfort assumptions were built around 1.0 clo — a person in a suit.
Almost nobody wears a suit now, and in any given office the range of clothing is wide. That matters more than most facilities managers realise:
- Where a dress code puts men in suits and women in dresses, the two groups can need air temperatures 2 to 4 °C apart to be equally comfortable. Same room, same thermostat, genuinely different requirements.
- Remove the dress code entirely and the range widens rather than narrows. The comfort gap across a mixed office can exceed 6 °C on clothing alone.
Add metabolic variation on top and the idea of one correct set temperature stops being achievable at all.
The way out
Two approaches actually work, and neither is “find the right number”.
Give people control. Fast-responding, zoned heating lets an individual adjust their own space rather than lobbying for the building. This is only practical with a system that responds in minutes — which rules out most high-mass systems and rules in radiant electric heating.
Design a range of environments. In a larger space, deliberately provide warmer and cooler areas and let people sit where suits them. It sounds like a compromise; in practice it satisfies far more people than a single averaged setting.
The one-size-fits-all thermostat fails most of the people in the room and wastes energy overshooting to placate whoever complains loudest. In a building with zoning and a system that reacts quickly, there is no reason to keep doing it.
Next in the series: humidity.
