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Heat bag

Coin activated heat pack (Sodium acetate)

Sodium acetate (C2H3NaO2) dissolved in water can be a supercooled liquid. By clicking with some kind of metal coin in the liquid, the crystallization can be started and that will release heat for about half an hour.
A small hand warmer of bad quality might stop releasing heat after 10 minutes. A large heat pack of good quality which is well covered with clothes might release a lot of heat for an hour.
The contents can be made liquid again by putting it in hot water of 80 °C to 100 °C (176 °F to 212 °F) for some time.

In 1977 a patent was applied for a heating pad with sodium acetate dissolved in water. The crystallization was initiated by bending a metal shape inside the bag. That patent has now expired.

I bought my first coin activated heat pack in 2003:
thermocomfort heat bag
Brand: THERMOcomfort©
This is a very pleasant heat bag. Through crystallization of the fluid in the cushion heat is created. By pressing some kind of coin in the cushion, the crystallization is started.
If I am cold, I just need to grab this cushion, press the coin, and then I put this pillow between my clothes.
It provides heat for relatively a long time.
The disadvantage is that it must be placed for about 20 minutes in hot water (close to boiling temperature), to liquefy the content. After that it can be used again.
The biggest advantage of this heat bag is, that it can not get too hot.
The quality of THERMOcomfort is a very good. It works reliable and heats up well and stays warm for a long time and after a lot of use it still gets just as warm.
This is what the website looked like:
In 2012, THERMOcomfort no longer seems to exist (the website was still online in 2020, but is abandoned).

In 2018 I bought a larger coin activated heat pack from the brand "WarmUp".
In the picture below is the "WarmUp" heat pack at the top and at the bottom are two "THERMOcomfort" heat packs.
WarmUp heat pack
Brand: WarmUp (, sold via
Price: 18 euros (in 2018)

According to the website of WarmUp, their reusable heat pack can be made liquid again by placing it in water of 80 °C (176 °F) for 20 minutes. That makes it possible to use a sous-vide cooker.


In 2020, I bought some WarmUp heat pads that I describe above.
They are 16 x 39 cm (6.3" x 15.3").
I made a vest for it with pockets on the back for the heating pads. I use this vest to go swimming when it is cold in the spring and in the fall.
heat pad WarmUp
Because the heating pads get a little above 50 °C (120 °F) it seems to be safer to prevent that they directly touch the skin. Therefor I used 2 mm (1/16 inch) thick synthetic 3D mesh fabric for the vest. I did not use normal fabric for the vest, because I wanted to be able to use it under my wetsuit when I go swimming.

One of the heating pads of WarmUp would hardly start. I received a new heating pad for it.
After that, it never happened again, and they always start.

I tried the "Heat In A Click" heat bags from and the Aidapt VM723B which I bought at
They did not stay upright in the vest, they collapsed. Therefor I could not use them in my vest.
Both came with a band for the waist. I made one band shorter to be able to use it around my neck to keep my neck warm.
In the photo below is the "Heat In A Click" on top, the "Aidapt" in the middle and at the bottom is the shortened band for my neck.
heatpack back

These prices are from 2020 in The Netherlands:
WarmUp          back heat bag  15.95 euros without waistband or 29.45 euros with waistband.
Heat In A Click back heat bag  27.50 euros inclusive waistband.
Aidapt VM723B   back heat bag  16.95 euros inclusive waistband.

The "WarmUp" has a stronger plastic bag and the coin has a plastic edge. The waistband is sold seperately for 13.95 euros. That makes a total of 29.45 euros.
The "Heat In A Click" starts too easily. When the coin scratches the inside of the plastic, it might already start.
The purple coloring of the "Adaipt" is too dark, making it sometimes hard to find the small coin. The waistband of the "Adaipt" is too small, it is not easy to put the bag inside the waistband.

After using them for a while, the "WarmUp" is obviously the best heat bag. The others sometimes start when I put them in my back pack. The coin to start them is easy to find with the "WarmUp" heat bag and not with the others.
According to "WarmUp, the plastic of their bag does not contain toxic chemicals such as softeners.

Clay heat bag

heat bag filled with clay heat bag Stadtholder moor
Brand and type: Stadtholder© Moor natural hot/cold pack 30x40cm
Price: 25,50 euros (in 2011).
This cushion is heated in the microwave. The cushion contains some kind of clay from Germany ("moor"), and heating it in the microwave works well.
It is easy to use, I put it a few minutes in the microwave, and then it is ready. I only have to remember the time to set the microwave to.
One time, the cushion was not completely cooled down and I wanted to heat it a little in the microwave. The cushion became very hot, but was still okay.
The cushion is flexible enough to place it on my neck.
After a few years of use, the plastic tore. That was because I folded it to get it into the microwave.

Because this heat bag is quite large, it is able to contain a lot of energy. I put it in the microwave for 6 or 7 minutes, and I turn the heat bag after 3 or 4 minutes.
This heat bag emits more heat during a longer time, and is therefor better than other heating pads.
In 2011 I bought my second heat pad of this type.
In 2016 I still use this heat pad.

Gel pack

gel hot pack gel hot pack
There are all kinds of gel packs. These are usually small. So they lose their heat quickly.

Single use heat pack

single use heat pack
A number of different brands of single use heat packs (or heat pads) are available. I bought one to test it.
After the heat pack is taken out of its packing, it becomes warm for more than one hour.
However it is only a little amount of heat, and the way it is used has a very big influence on the temperature. Therefore it is not very pleasant to use.

Below is a photo of a single use heatpack from Hansaplast:
hotpack hansaplast

Cherry pit heat pad

cherry pit heat pad cherry pit heat pad
Brand: Hittepit.
Price: 20 euro.
Weight: 1050 grams.
This cherry pit heat pad must be moisturized, after that I put it in the microwave for 3 minutes. It stays warm for a long time.
It can't get as hot as the clay heat bag, so the heat doesn't get very deep.
After using it a few times, a seam tore and the cherry pits fell out. So the quality was a disappointment.

Below is a cheap cherry pit heat pad:
cherry pit heat pad
Weight: 425 grams.
This cheap cherry pit heat pad is probably too dry, in the microwave it gets too hot very quick, en it stays warm for only a short time.

Last change to this page: July 2021