It probably isn't a surprise that natural cork is environmentally friendly, but with the trend toward using screwcaps for wine bottle closures, it is necessary to look at how they impact the environment. According to research conduceted by a French closure company, the screwcaps are the worst of the lot and leave the largest carbon footprint compared to regular cork and synthetic closures.

From Decanter:

The production of screwcaps gives off over 10kg of CO2 per tonne compared with 2.5kg of CO2 per tonne for corks, according to tests conducted by Cairn Environment for Oeneo Bouchage in France.

The composite DIAM closure fell between the two, with a carbon footprint of 4.3kg of CO2 per tonne.

All the closures are produced by Oeneo, and production of the PVC capsule to go with the cork and DIAM closures was taken account in recording the data.

Oeneo Bouchage, which makes the DIAM composite and treated cork closure, said the tests had been ratified by the French Environmental Agency.