screwtop

A screwtop, also known as a screw cap, is a closure for bottles and jars that relies on matching threads on the cap and the container mouth. Turning the cap causes it to advance along the threads and compress a seal to keep contents in and air out. Screwtops are widely used on glass, plastic, and metal containers for beverages, food, cosmetics, and pharmaceuticals.

Construction: Caps are typically made of plastic (such as polypropylene) or metal (aluminum or tinplate) and are paired with liners made of polyethylene foam, rubber, or paper. The liner improves sealing, provides barrier properties against moisture and oxygen, and can carry branding. Some caps include tamper-evident bands.

Advantages and limitations: Screwtops offer a reliable, resealable seal that is easy to open and reclose and are compatible with automated filling lines. They can reduce cork taint in wine and are generally cost-effective. Limitations include potential cross-threading, the need for proper torque, variable oxygen transmission depending on liner, and consumer perceptions of prestige compared with cork closures.

Variants and features: Common variants include continuous-thread designs and multi-turn caps, child-resistant closures for medicines, tamper-evident seals, and sport caps or pour spouts. Some wine closures use polymer or composite liners instead of natural cork.

History and use: Screw closures emerged in the 19th century and gained widespread use in the late 20th century. They are now standard on many drinks bottles, jars, and cosmetic containers, and remain a common alternative to cork or other closures.