Leaching is the release or movement of substances from a material into its surroundings, often when a liquid such as water contacts it. In plastics, this can involve additives or other compounds migrating out of the material. Whether it occurs, and how much, depends on factors such as the material’s composition, exposure conditions, and duration.
Leaching matters because released substances may affect water quality, material performance, or the suitability of a product for its intended use. It is distinct from a material simply dissolving or chemically breaking down. In practice, engineers assess leaching under relevant conditions rather than assuming a material is inert; measurements can help identify what is released and at what levels.