gelpacks

A gelpack is a flexible pouch filled with a gel or liquid mixture used to provide cooling or heating for medical, commercial and recreational purposes. Gelpacks are commonly used in first aid to reduce swelling and pain, in food and pharmaceutical shipping to maintain cold-chain temperatures, and by consumers for lunchboxes and personal therapy.

Types include reusable cold packs (freezer packs) containing water-based gels thickened with polymers or cellulose and often blended with propylene glycol or glycerin to lower freezing point; instant cold packs that produce an endothermic reaction when a inner pouch is broken (typically water mixed with ammonium nitrate or urea); and reusable heat packs that rely on materials such as supersaturated sodium acetate solutions or microwaveable starch-based gels.

Composition varies by application: reusable packs typically use non-toxic, water-retaining polymers or hydrogels inside a puncture-resistant plastic envelope, while single-use instant packs use chemical salts that absorb heat during dissolution. Many gelpacks are designed to be non-toxic, but leaking contents can irritate skin or contaminate food, so manufacturer instructions should be followed.

Advantages include conformity to body contours, relatively long thermal retention compared with ice, and reusability for certain types. Limitations include potential for puncture and leakage, reduced effectiveness as the temperature equalizes with surroundings, and environmental concerns over plastic waste and disposal of chemical contents. Proper handling, storage, and disposal according to manufacturer guidance reduce safety and environmental risks.