What the heck is a CLO?
You may have read or heard something about CLO, and even some buying guides and product literature may reference CLO or CLO value. Developed in 1941, it was the first real attempt to explain the insulation value of clothing so people would know how much clothing they might need to stay warmer or cooler in a given temperature environment. A CLO value of 1 is defined as the amount of clothing required by a resting human (in other words, sitting, lying down or standing, but not moving) to be comfortable at a room temperature of 21 degrees C, or approximately 71 degrees F. That single value of CLO is equivalent to a typical business suit worn by a man -- shirt, undershirt, trousers and suit jacket. The higher the CLO number, the more insulating value is provided.
Yeah, but who hikes in a business suit?
Not many folks. But it is a good point of reference. Think of it like this: If something has a CLO value of 2, it means it provides the same amount of insulation as two suits. All garments and even sleeping bags carry a CLO value. As a point of comparison, the Department of Performance Textiles at Leeds University in the United Kingdom developed a comfort model to relate the thermal resistance of sleeping bags to temperature ratings. The study found that a CLO value of 2.5 was needed to keep a sleeping person comfortable at an air temperature of 59 degrees F, or 15 degrees C. A CLO value of 4 was required for comfort at 48.2 degrees F, or 9 degrees C. Thirty-two degrees F, or 0 degrees C, you'd need a CLO value of 6.
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