Cork is an impermeable, buoyant material comprised of bark tissue that has been harvested and refined for commercial use. The medium cork stoppers in this Hillman assortment have a tapered shape to provide a secure seal in various-sized containers. The natural cork construction can be cut to an exact length, and its natural elasticity helps form a tight seal. Commonly used as bottle stoppers. Full assortments of #52009 feature Hillman item numbers #52010 & #52011.