Cork is the bark of the cork oak, stripped on a roughly nine-year cycle without harming the tree. It is elastic, impermeable and insulating.
It replaces plastic and aluminium closures, EVA foam in footwear and yoga mats, flooring underlay, insulation and some rigid packaging. Corticeira Amorim (Portugal) is by far the largest producer and also makes cork-polymer compounds that cut plastic volume by up to 60 percent.
Amorim's commissioned life-cycle assessment (LCA) reports that natural cork stoppers have a negative carbon balance once cork-oak sequestration is counted, and that plastic stoppers carry about ten times the carbon dioxide (CO2) of cork. This is a vendor-commissioned study; no independent LCA was found. Cork is renewable and recyclable through specialist schemes.
Drawbacks: supply is concentrated in the Iberian peninsula; cork composites are often bound with polymer, so a cork product is not automatically plastic-free; the long harvest cycle limits how fast supply can grow. No public cost comparison was found.