What are hot packs primarily filled with?

Hot packs are primarily filled with silica gel, which is a desiccant made of silicon dioxide. Silica gel is chosen for its ability to retain heat effectively, providing a consistent and prolonged thermal application when activated by water or heat. When heated, the silica gel can store and release heat efficiently, making it suitable for use in therapeutic hot packs that aim to promote muscle relaxation, improve blood flow, and alleviate pain.

Other common fillers for hot packs, such as water or clay, do exist, but they may not provide the same level of stability in terms of heat retention and distribution that silica gel offers. Additionally, sand packs can be used, but they do not heat up as evenly or retain heat as effectively. Air is not used as a filler for hot packs, as it does not possess the qualities required to provide therapeutic heat. Thus, silica gel stands out as the ideal material for maximizing the benefits of hot therapy.