Hand warmers are small (mostly disposable) packets which are held in the hand and produce heat on demand to warm cold hands. They are commonly used in outdoor activities. Other types of warmers are available to provide soothing heat for muscular or joint aches.

History

The hand and foot warmer was first patented by Jonathan T. Ellis of New Jersey in 1891, though no evidence exists that it was ever produced. The first commercially produced hand warmer was created by Japanese inventor Niichi Matoba. Matoba received a patent for applying the principle of an oxidation reaction that produces heat by means of platinum catalysis. He then devoted his time to researching how to make the product suitable for practical use. In 1923, he manufactured a prototype of his device naming it HAKUKIN-kairo (HAKKIN warmer). A version of these original portable hand warmers is still produced in Japan.

Types

Air activated (iron)

Air-activated hand warmers contain

cellulose Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall ...

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...

activated carbon Activated carbon, also called activated charcoal, is a form of carbon commonly used to filter contaminants from water and air, among many other uses. It is processed (activated) to have small, low-volume pores that increase the surface area avail ...

vermiculite Vermiculite is a hydrous phyllosilicate mineral which undergoes significant expansion when heated. Exfoliation occurs when the mineral is heated sufficiently, and commercial furnaces can routinely produce this effect. Vermiculite forms by the wea ...

(which holds water) and

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...

and produce heat from the

exothermic In thermodynamics, an exothermic process () is a thermodynamic process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in a form of light (e.g. a spark, flame, or flash), electricity (e ...

oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...

of iron when exposed to

air The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing f ...

. They typically emit heat for 1 to 10 hours, it usually takes 15–30 minutes to start to heat up, although the heat given off rapidly diminishes after 1–2 hours. The

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

molecules in the air react with iron, forming rust. Salt is often added to catalyze the process.

Supersaturated solution (crystallisation-type)

This type of hand warmer can be recharged by immersing the hand-warmer in very hot water until the contents are uniform and then allowing it to cool. The release of heat is triggered by flexing a small metal disk in the hand warmer, which generates

nucleation In thermodynamics, nucleation is the first step in the formation of either a new thermodynamic phase or structure via self-assembly or self-organization within a substance or mixture. Nucleation is typically defined to be the process that deter ...

centers that initiate crystallisation. Heat is required to dissolve the salt in its own water of crystallisation and it is this heat that is released when crystallisation is initiated. The

latent heat of fusion In thermodynamics, the enthalpy of fusion of a substance, also known as (latent) heat of fusion, is the change in its enthalpy resulting from providing energy, typically heat, to a specific quantity of the substance to change its state from a s ...

is about 264–289 kJ/kg. This process can be scaled up to create a means of domestic heating storage and can produce instant heat.

Lighter fuel

Cigarette lighter fuel hand-warmers use lighter fluid (highly refined

petroleum naphtha Petroleum naphtha is an intermediate hydrocarbon liquid stream derived from the refining of crude oil with CAS-no 64742-48-9. It is most usually desulfurized and then catalytically reformed, which rearranges or restructures the hydrocarbon mole ...

), in a catalyst combustion unit that runs at a lower temperature than an open flame with a greatly reduced fire risk. After lighting they operate inside a fabric bag typically with a drawstring. This controls the oxygen supply to the catalyst and protects against skin burns. Re-use is simply by refuelling. Current units use a glass fiber substrate coated with platinum. Low cost Chinese units may use other cheaper catalysts that don't work as well. Some older units used asbestos substrates. The replaceable catalyst unit last for many years provided they have combusted vapour from their cotton wadding filled fuel reservoir, and have not had fuel directly applied to them. These hand warmers are for people who work or pursue leisure activities outdoors in very low temperatures, especially those that require manual dexterity that is not possible while wearing thick gloves or mittens. They date from the foundation of the Japanese Hakkin company by Niichi Matoba, who founded it to produce a hand warmer 'Hakkin Kairo' based on his Japanese patent of 1923. John W. Smith, President of Aladdin Laboratories, Inc. of Minneapolis was awarded a US patent for a product called the Jon-e (pronounced “Johnny”) catalytic hand warmer on December 25, 1951. Production peaked in the fifties and sixties, at 10,000 warmers a day. Aladdin went out of business in the 1970s. In 2010 the Zippo lighter company introduced an all-metal catalytic hand warmer, along with other outdoor products.

Battery

Battery operated hand warmers use electrically resistive heating devices to convert electrical energy in the battery into heat. Typically hand warmers can heat for up to six hours, with heat outputs from 40-48C. Rechargeable electronic hand warmers can be charged from a mains power supply or from a 5V USB power supply, with up to 500 recharge cycles possible.

Charcoal

Charcoal Charcoal is a lightweight black carbon residue produced by strongly heating wood (or other animal and plant materials) in minimal oxygen to remove all water and volatile constituents. In the traditional version of this pyrolysis process, cal ...

hand-warmers provide heat by burning charcoal in a special case. These can last up to 6 hours and become comfortably hot. Charcoal cases for these usually have felt on the outside and have items in it that do not produce heat, but spread the heat such as metal. A charcoal hand warmer can start heating when both ends of charcoal are struck and then extinguished to create a hot charcoal. The smouldering stick is then placed inside the case. The charcoal sticks are available from most outdoor activity shops and are fairly inexpensive.{{Citation needed, date=December 2018

References

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