The stoppers that have been traditionally used in wine bottles have been made from the bark of the Cork Oak ~Quercus suber.
While it has many advantages including allowing the wine to "breath" a fungi in the bark can give an unpleasant taste to the wine - it becomes "corked". Screw tops and plastic bungs have been the alternative stopper but both prevent the wine from breathing and have been largely rejected by higher price producers. This "cork" answers many of these problems. It is a plant based polymer; the structure (background) allows the wine to breath; it can be recycled; it does not host fungi that, reacting with chlorides in winery sanitation / sterilization products, produces TCA (2,4,6 - trichloroanisole) that taints the wine. These artificial corks have a user life of up to 25 years.