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Coffee Joulies are small, stainless-steel capsules of phase change material designed to be placed in a covered, insulated container cup of coffee to keep it at a drinkable temperature for a longer period of time. They came out of a Kickstarter project launched by Dave Petrillo and Dave Jackson in Tahoe City, California.
The Kickstarter project launched around March 27, 2011 and was fully funded three days later, even though the funding target didn't need to be met for thirty days. Production was established at Sherrill Manufacturing in Sherrill, New York. The team decided to continue with production in the United States, rather than moving to Mexico, as was their initial plan.
The project was at 300% of the target funding level by April 1, 2011. As of 9 April 2011[update], the project had raised $128,000 by 2200 backers, while the original project target was only $9500, and the dies for stamping were expected to cost $20,000.
The non toxic Paraffin wax has a melting point of 140 °F (60 °C). A similar concept using phase change materials, but integrated into the walls and bottom of a cup, had been invented by the Fraunhofer Institute for Building Physics two years earlier.
Coffee Joulies are best used in an insulated vessel. The more efficient the insulation, the more effective Joulies will be. They are most effective in a vacuum thermos bottle or insulated cup with a lid (such as the often-used, foam take-away cups). Taking a thermos of coffee to work (or commuting, camping, fishing, etc.), to be consumed over a number of hours is an excellent and highly-effective use of Joulies.
Using Joulies in an open, ceramic coffee cup will bring the temperature down to a drinkable level without blowing on the beverage or using a spoon to cool it down. The benefit of keeping the coffee at a drinkable temperature is diminished because of the heat loss through the ceramic material itself and exposure of the coffee to the air.
A video has been released by the creators that shows the initial cooling effect, but ends shortly after that, failing to show the effect of keeping the beverage hot for significantly longer.
Some reviews show Joulies work while others have expressed doubts over the product's effectiveness. After doing some tests, they reported that the product does not work very well if at all.  Specifically it is stated that the promised effect, while existing, is "barely noticeable", especially when compared to adding other objects of similar heat capacity, thus being far from the creators' claims that the drink “will be ready to drink three times sooner and will remain hot twice as long.”