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An ice pack or gel pack is a portable bag filled with water, refrigerant
gel A gel is a semi-solid that can have properties ranging from soft and weak to hard and tough. Gels are defined as a substantially dilute cross-linked system, which exhibits no flow when in the steady-state, although the liquid phase may still dif ...
, or liquid, meant to provide cooling. They can be divided into the reusable type, which works as a
thermal mass In building design, thermal mass is a property of the mass of a building that enables it to store heat and provide inertia against temperature fluctuations. It is sometimes known as the thermal flywheel effect. The thermal mass of heavy structura ...
and requires freezing, or the instant type, which cools itself down using chemicals but can only be used once. The instant type is generally limited to medical use as a cold compress to alleviate the pain of minor injuries, while the reusable type is both used as a cold compress and to keep food cool in portable
cooler A cooler, portable ice chest, ice box, cool box, chilly bin (in New Zealand), or esky ( Australia) is an insulated box used to keep food or drink cool. Ice cubes are most commonly placed in it to help the contents inside stay cool. Ice packs a ...
s or in
insulated shipping container Insulated shipping containers are a type of packaging used to ship temperature sensitive products such as foods, pharmaceuticals, organs, blood, biologic materials, vaccines and chemicals. They are used as part of a cold chain to help maintain pr ...
s to keep products cool during transport.


Reusable packs

To be prepared for use, the pack is first placed in a freezer. Both
ice Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaqu ...
and other
non-toxic Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subs ...
refrigerants (mostly water) can absorb a considerable amount of heat before they warm above .` Ice packs are used in coolers to keep perishable foods (especially meats, dairy products, eggs, etc.) below the danger zone when outside a refrigerator or freezer, and to keep drinks pleasantly cool. The amount of ice needed varies with the amount of food, its initial temperature, the thermal insulation of the cooler, and the ambient temperature and exposure to direct sunlight. Ice initially well below freezing temperature will last a little longer. Water has a much higher latent heat of fusion than most substances, and a melting temperature which is convenient and easily attained with, for example, a household freezer. Additives to improve the properties of water are often used. For example, substances can be added to prevent bacterial growth in the pack, or to prevent the water from solidifying so it remains a thick gel throughout use. Gel packs are often made of non-toxic materials that will remain a slow-flowing gel, and therefore will not spill easily or cause contamination if the container breaks. Gel packs may be made by adding hydroxyethyl cellulose,
sodium polyacrylate Sodium polyacrylate (ACR, ASAP, or PAAS), also known as waterlock, is a sodium salt of polyacrylic acid with the chemical formula ˆ’CH2−CH(CO2Na)−sub>n and has broad applications in consumer products. This super-absorbent polymer (SAP) ha ...
, or vinyl-coated
silica gel Silica gel is an amorphous and porous form of silicon dioxide (silica), consisting of an irregular tridimensional framework of alternating silicon and oxygen atoms with nanometer-scale voids and pores. The voids may contain water or some other l ...
.


Hot-or-cold packs

Hot-or-cold packs are ice packs that are rated for high temperature use. They can be used as a normal reusable ice pack by storing in a freezer, but they can also be heated in water or a microwave oven to reach the desired temperature. The first hot and cold pack was introduced in 1948 with the name ''Hot-R-Cold-Pak'' and could be chilled in a refrigerator or heated in hot water. The first reusable hot cold pack that could be heated in boiling water or a
microwave oven A microwave oven (commonly referred to as a microwave) is an electric oven that heats and cooks food by exposing it to electromagnetic radiation in the microwave frequency range. This induces polar molecules in the food to rotate and produce ...
was first patented in 1973.


Instant ice packs

An instant cold pack is a single-use device that consists of two bags; one containing
water Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...
, inside a bag containing
ammonium nitrate Ammonium nitrate is a chemical compound with the chemical formula . It is a white crystalline salt consisting of ions of ammonium and nitrate. It is highly soluble in water and hygroscopic as a solid, although it does not form hydrates. It is ...
, calcium ammonium nitrate or
urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important ...
. When the inner bag of water is broken by squeezing the package, it dissolves the solid in an
endothermic process In thermochemistry, an endothermic process () is any thermodynamic process with an increase in the enthalpy (or internal energy ) of the system.Oxtoby, D. W; Gillis, H.P., Butler, L. J. (2015).''Principle of Modern Chemistry'', Brooks Cole. p. ...
. This process absorbs heat from the surroundings, quickly lowering the pack's temperature. Instant cold packs are a convenient replacement for crushed
ice Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaqu ...
used as
first aid First aid is the first and immediate assistance given to any person with either a minor or serious illness or injury, with care provided to preserve life, prevent the condition from worsening, or to promote recovery. It includes initial in ...
on sport injuries or
heat illness Heat illness is a spectrum of disorders due to increased body temperature. It can be caused by either environmental conditions or by exertion. It includes minor conditions such as heat cramps, heat syncope, and heat exhaustion as well as the mo ...
, and can be carried as first aid to remote or wilderness areas where ice is unavailable. However, they do not provide as much or as long-lasting cooling as ice.


Safety concerns

Gel packs have been made with
diethylene glycol Diethylene glycol (DEG) is an organic compound with the formula (HOCH2CH2)2O. It is a colorless, practically odorless, and hygroscopic liquid with a sweetish taste. It is a four carbon dimer of ethylene glycol. It is miscible in water, alcohol, ...
and
ethylene glycol Ethylene glycol (IUPAC name: ethane-1,2-diol) is an organic compound (a vicinal diol) with the formula . It is mainly used for two purposes, as a raw material in the manufacture of polyester fibers and for antifreeze formulations. It is an odo ...
. Both can cause illness if ingested in large amounts, making them unsuitable for use with food. The US Consumer Product Safety Commission recalled such packs.


See also

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Cryotherapy Cryotherapy, sometimes known as cold therapy, is the local or general use of low temperatures in medical therapy. Cryotherapy may be used to treat a variety of tissue lesions. The most prominent use of the term refers to the surgical treatment, s ...
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Hot pack A heating pad is a pad used for warming of parts of the body in order to manage pain. Localized application of heat causes the blood vessels in that area to dilate, enhancing perfusion to the targeted tissue. Types of heating pads include electri ...
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Hand warmer 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 ...
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Hilotherapy Cold compression therapy, also known as hilotherapy, combines two of the principles of rest, ice, compression, elevation to reduce pain and swelling from a sports or activity injury to soft tissues and is recommended by orthopedic surgeons follow ...
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Phase-change material A phase change material (PCM) is a substance which releases/absorbs sufficient energy at phase transition to provide useful heat or cooling. Generally the transition will be from one of the first two fundamental states of matter - solid and liq ...
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Enthalpy 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 ...


References

{{DEFAULTSORT:Ice Pack Medical treatments Cooling technology Food preservation Medical equipment Cryotherapy Packaging