Imagine all of the possible applications of a heating pad that doesn’t have to be plugged in, doesn’t have to be filled with hot water, doesn’t have to be heated in a microwave, heats to a safe preset temperature in under two minutes, and is reusable hundreds and hundreds of times.

Doctor Down Thermo-Pad

What is in the pad?
The pad contains water, food grade sodium acetate trihydrate (an ingredient in salt and vinegar potato chips) and a stainless steel disc. When the pad is in its liquid state it is a “super saturated” solution.

Why won’t the pad activate?
The Thermo-Pad must be in its liquid state and below 50° C (122° F) before it will activate. If the pad is too hot it will not activate. When you activate a warm pad, it will not crystallize and turn white; the pad will go cloudy and remain mostly liquid, this is because only the liquid that is below 54° C (130° F) will crystallize and the rest will remain liquid to generate heat as the pad cools. In this way a warm pad will remain near its maximum temperature until all of the liquid has crystallized. Occasionally it may require a few flexes of the disc but the pad should activate.

How is the heat produced?
Flexing the metal disc in the liquid pad creates a seed crystal that starts a chain reaction causing the pad to crystallize. This crystallization ALWAYS occurs at a temperature of 54o C (130° F) The pad will not activate if it is above this temperature. Video of Thermo-Pad being activated

Once activated, the Thermo-Pad has available to it a predetermined amount of energy. It will use this energy to increase the temperature of the pad to 54o C and use whatever is left to maintain that temperature. This ability to produce heat for a period of time is accomplished because all of the liquid does not crystallize immediately. Molecules that were not required to heat the pad to its maximum temperature will remain liquid, and crystallize as required, to maintain the maximum temperature. This means that a pad that is warm will maintain its maximum temperature longer than one that is cold.

How do you reuse the pad?
Once the Thermo-Pad has given off all of its heat it will remain in its crystallized state until it is recharged. This is accomplished by placing the crystallized pad in boiling water for 5 to 20 minutes (depending upon the size of the pad) until all of the crystals are melted. Once completely liquefied, remove the Thermo-Pad from the water and store it until it is required. The Thermo-Pad should remain liquid as it cools. If crystals form as the pad cools it has not been boiled long enough and should be re-boiled.  Another method for those of you who have newer dish washers, is to put the pads on the top rack and run them through on the “sani cycle”. Video of Thermo-Pad being recharged

How long does the heat last?
Depending on its size, starting temperature and insulation, a Thermo-Pad will provide heat from 15 minutes to 6 hours. Starting at room temperature and used as a heating pad, a well insulated Model  808 Thermo-Pad will remain at its maximum temperature for approximately one hour and slowly cool to room temperature in about three to four hours. If you use the pad immediately after it has been recharged, (wrap it in an extra layer of towel as it may be very hot) it will give off heat as it cools and then may be activated while still warm. In this way an 808 pad may last as long as 6 hours.

How many times can they be used?
There is no limit as to the number of times a Thermo-Pad can be used. There are pads still in use after eighteen years. The pad will not operate if there is a hole in the vinyl. Thermo-Pad is manufactured from the same vinyl as is used in water beds and comes with a one year warranty.

What are the white crystals that form in the liquid pad?
If the Thermo-Pad has been stored in its crystallized state for an extended period of time, a small amount of water can evaporate from the pad and cause the solution to become more concentrated. This higher concentration is indicated by “snowflake like” crystals in the liquid pad. The pad will still operate but at a slightly higher temperature. This water loss can be substantially reduced by storing the pad in its liquid state and may be reversed by extending the boiling times and by leaving the pad in water to cool.

What happens if the pad gets a hole in it?
If  a liquid Thermo-Pad gets a hole in it, it will activate. The pad is then not able to be recharged and may be disposed of with normal garbage. The contents are not dangerous and may be dealt with as if you were dealing with normal salt.

What is the best way to use the pad outdoors when it’s cold?
Just before you go out, pre-heat the liquid Thermo-Pad in a sink of hot water. (the hotter the better) Store the pad as close to your body as possible (don’t activate the pad) and you can use this heat to keep you warm as the pad cools. Once the pad has cooled to a point where you are getting cold, activate the liquid pad and it will heat to keep you warm longer.
Please note that vinyl gets brittle when it gets very cold and can be easily damaged.