Size 4 Pure Gum Rubber Stoppers will plug food containers, lab vials and other openings. Pure Gum Rubber useful to 220º F and in applications with moderate chemicals, alocohols and organic acids. Do not use with strong acids, fats, grease or hydrocarbons. Not for food or beverage packaging applications.
Looks like cork
Using these for bottle light stoppers for patio project. And the Gum Rubber Stoppers look a lot like cork which adds a better look to the project than say black or white stoppers.