Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A screw cap is a metal cap that screws onto threads on the neck of a bottle, generally with a metal skirt down the neck to resemble the traditional wine capsule ("foil"). A layer of plastic (often PVDC), cork, rubber, or other soft material is used as wad to make a seal with the mouth of the bottle. Its use as an alternative wine closure is gaining increasing support as an alternative to cork for sealing wine bottles. The most known brand of wine screw caps is Stelvin, a brand of Rio Tinto Alcan. The brand is so common that it is genericized in common use, with many in the wine trade referring to screw caps as "Stelvin closures", regardless of brand.