A blister pack is pre-formed plastic packaging used for small consumer goods, foods, and for pharmaceuticals. The blister pack contains a cavity or pocket made from thermoformed plastic. This usually has a backing of paperboard or a lidding seal of aluminum foil or plastic. A blister that folds onto itself is often called a clamshell.
Blister packs are useful for protecting products against external factors, such as humidity and contamination for extended periods of time. They are commonly used for medication because they are secured by a strong, paper-backed foil that protects the pills until dispensed. Opaque blisters also protect light-sensitive products against UV rays.