A study done by the consultancy firm PriceWaterhouseCoopers has shown that natural cork closures on bottles are the most environmentally friendly closure: synthetic (plastic) corks were deemed nine times more damaging to the environment and screw caps twenty two times more. The study was commissioned by Amorim, the world’s largest cork manufacturer, but is said to have adhered to strict scientific principles, including peer review and involvement of representatives from manufacturers of alternative closures.