Closures are devices and techniques used to close or seal a bottle, jug, jar, tube, can, etc. Closures can be a cap, cover, lid, plug, etc.
Other types of containers such as boxes and drums may also have closures but are not discussed in this article.
Many containers and packages require a means of closing. It can be a separate device or seal or sometimes a integral latch or lock. Depending on the contents and container, closures have several functions:
Many types of packaging with their closures are regulated for strength, safety, security, communication, recycling, and environmental requirements.
Closures need a means of attaching to the container with sufficient security. Threads, lugs, hinges, locks, adhesives, etc. are used.
Many closures need to have the ability to adjust to slight manufacturing variation in the container and the closure structure. Some closures are made of flexible material such as cork, rubber, or plastic foam. Often an o-ring or a closure liner (gasket made of pulp or foam cap liner) is used. Linerless closures often use a deformable plastic rim or structure to maintain the seal.