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Cooling vests are designed to provide protection against heat. They are commonly used by personnel working under extreme conditions and high temperatures such as firefighters, athletes, fishermen, hunters, police officers, military personnel, and people with health problems. (They also exist as dog cooling vests.) There are four main types:
- Evaporative vests that use evaporation to cool the body down
- Cold pack vests
- Active vests
- Phase change vests, which is our subject here
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How Phase Change Cooling Vests Work
Phase change cooling vests use a special thermal energy storage material or phase change material (PCM) to maintain their cooling properties. This material is sealed in leak-proof inserts or packs made of durable plastic that can be cooled down by being soaked in ice water for a few minutes. The PCM inside the packs becomes solid and ready to be placed inside the pockets of the vest.
For the next two to three hours, the PCM will absorb the heat generated by the body until it becomes liquid again. Throughout this period of time, it maintains a constant temperature of approximately 40 to 65 degrees Fahrenheit, depending on the manufacturing design. As soon as the PCM becomes liquid again, it will have to be recharged, and this procedure can be repeated again and again. Since their cooling temperature is above that of freezing water, they don't require a freezer. Instead, they can be recharged in ice water or another cool liquid that is more practical to find.
The cooling inserts or packs are produced in a variety of shapes and sizes in order to fit in the vest pockets. Each vest may typically accommodate four inserts and has adjustments, e.g. zippered pouches, for the packs to fit in. This way the packs are held steadily in place for as long as they absorb the body's heat. The design of the vest allows the cool packs to come into direct contact with the skin, while an upper insulation layer prevents external heat from being absorbed by the PCM.
In order to extend the cooling duration, it is possible to use two sets of cooling packs alternatively. As soon as the first set has absorbed the body's heat, the second set will be already recharged and ready to use. The cycle can be repeated as many times as the user desires. It is also possible to put two packs in each pocket in order to extend their duration. The weight of a vest holding a single set of cool inserts is approximately 5lbs, making it a light and practical garment for any user to wear.
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A Sampling of Commercially Available PCM Cooling Vests
This vest is adjustable at the sides and shoulders with a zipper-pull front. It can deliver a constant temperature of 58 degrees Fahrenheit for three hours. It is available from Polar Products.
Phase Change Cooling Traffic Safety Vests provided by TechKewl.
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The PCM has special benefits when compared to other cooling materials such as water. It is lighter that water when cooled and feels more natural when it is close or in touch with the skin (no feel of frostbite), delivering a constant temperature of approximately 58-65 degrees F. The PCM can last considerably longer than ice- almost 3 hours- and is not affected by humidity conditions. Moreover, the cooling packs present certain desirable properties: they are practical and reusable, they have the ability to expand in order to resist bursting, and they absorb shocks.
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Next Generation PCM Cooling Vests
New PCM cooling vests have become available recently. Glacier Tek’s “renewable phase change material" (RPCM) cooling vests use a special “green" bio-material made from processed fats and oils instead of petroleum byproducts. These vests maintain a temperature of 59°F (15°C) and recharge after twenty minutes in ice water. It is possible to be worn directly against the skin as the PCM and since they are environmentally friendly, they don't cause any skin damage or irritation in the event of leaks.