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How your body uses and loses heat
Scientists have found that the human body sitting at rest consumes 4.7 kilocalories/hour/square foot of body surface area and transfers this energy into heat.
When thinking about heat loss, it is important to remember that heat loss is affected by:
- body temperature
- outside air temperature and wind speed
- distances between the insulation fibers
- thickness of insulation
- fiber size
Clo Defined
The clo unit is defined as the amount of clothing required by a resting subject to be comfortable at a room temperature of 70°F (21°C). Clo-value is analogous to R-value for rating house insulation. For example, 1 R-value = 1.137 clo-value.
Normal Clo Values
Nude person clo = 0.0
Typical business suit clo = 1.0
Clo Vaues are Additive
Summing the clo values of individual components will approximate the total system clo.
Determining Effective Clo
Total clo is estimated by adding the clo values of the components and correcting for surface area, fit, and air layer effects. This procedure was developed by the American Society of Heating, Refrigeration and Air conditioning Engineers.
Effect of Activity Level
The insulation required by an individual to maintain comfort is markedly affected by activity level. This factor must be considered when choosing a garment for a particular activity.
Staying Warm
Thermal comfort is achieved by balancing three factors:
- rate of heat production by your body
- insulation value of your clothing (clo)
- environmental temperature
Of those three, it's easiest to alter the insulation value of your clothing. To do this we need to understand how, exactly, insulations work.
Insulations work in two ways: first, by trapping air. The more air trapped, the more efficient the insulation. Second, by reflecting back the body’s radiant heat.
The unique microfibers of Thinsulate™ Insulation are about ten times smaller than the fibers of most other synthetic insulations, which means they’re much more efficient at trapping air. . . and more effective at keeping you warm. It also means we can pack more fibers into the same space, where they can reflect back more of the body’s radiant heat.
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The fibers of Thinsulate™ Insulation are fine, making them ideal for trapping insulating air and reflecting back the body's radiant heat. |
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The fibers in 6-denier polyester are much thicker and not nearly as efficient at trapping air or reflecting back body heat. |
Neither repeated machine washings nor dry-cleanings markedly affect the performance of Thinsulate insulation. Tests have shown, in fact, that Thinsulate insulation’s average “clo” (a measure of the ability of an insulation to keep you warm) remains relatively unchanged even after repeated cleanings.
Thinsulate insulation is the smartest choice if staying warm is important to you. When you compare equal thicknesses, the original "warmth without bulk" Thinsulate insulation offers almost one-and-one-half times the warmth of down, and twice the warmth of other high-loft insulation materials.
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