Heat packs (also called “kairo” in Japanese) are dispensable items in Japan during the colder months. They are designed to be placed in a jacket pocket or in shoes to keep your body warm. Kairo were invented by a Japanese company.
■ Type of Heat packs
Heat packs essentially come in two main forms: adhesive type and non-adhesive type or pocket type.
The regular size is about 10cm in height and 15cm in width.
The small size is about 7cm in height and 10cm in width.
■ How to use
Heat packs are commonly used in outdoor activities such as hiking and skiing to keep extremities warm. It works when the plastic cover is opened and it touches air. It gets warm quickly when shaken well. It is designed to become as warm as about 60 degrees and to last for 20 hours or so.
■ Invented by a Japanese company
Ingredients are Iron powder, Activated carbon, Salts, Wood powder, Absorbent resin, Vermiculite, and water.
Back in the mid-1970s, a company called Lotte is said to have invented this product. Lotte’s main business is making chewing gum and chocolates. They originally tried to develop a powerful oxygen absorber, using iron powder, to put in small sachets in its bags of confections to stop them going stale. By accident, water got mixed into the iron, and it got warm.
To the dismay of Lotte engineers, the iron-powder heat pack itself could not be patented because its chemical formula is considered too general.
■ Big market
Today many companies make and sell heat packs that work through the same chemical reaction.
According to Nihon Kairo Kogyokai, an industry association of 18 major disposable heat pack manufacturers, a total of 1.4 billion heat packs were sold and the market size was over 30 billion yen in 2013.
There are many brands. Hokaron is a product of Lotte. Hokkairo is that of Hakugen. There are Kiribai kairo, Iris kairo and more.
■ Export to overseas
Some companies have exported to some countries.
In America, heat packs are called disposable hand warmers and they sell well in such cities as New York and Chicago. In China, a popular brand is called Nuan-pao-pao（暖宝宝）in Chinese, which literally means a warm baby. Thanks to the charming name, Nuan-pao-pao are very popular. In Russia, the Russian police purchased for traffic police officers in large quantities.
You can buy it at a supermarket or a convenience shop. To avoid burns to skin, you must not attach a heat pack to the direct skin, please use it very carefully.