Cork

Cork is a material harvested for commercial use from primarily cork oak. Because of its impermeable, buoyant, elastic, and fire retardant properties, it is used in a variety of products, the most common of which is wine stoppers.

The cork industry is generally regarded as environmentally friendly. Cork production is generally considered sustainable because the cork tree is not cut down to obtain cork; only the bark is stripped to harvest the cork. The tree continues to live and grow. The sustainability of production and the easy recycling of cork products and by-products are two of its most distinctive aspects. Cork oak forests also prevent desertification and are a particular habitat in the Iberian Peninsula and the refuge of various endangered species.

https://www.zmescience.com/ecology/green-living/cork-what-is-the-material-we-stuff-our-wine-bottles-with/