These high quality cork stoppers are an economical alternative to rubber stoppers Safe for use with food or drink! These are real corks harvested from the the outer bark of an evergreen type of oak tree called the cork oak (species Quercus suber) that is native to the Mediterranean region. Cork is an impermeable buoyant material, the phellem layer of bark tissue that is harvested for commercial use primarily from Quercus suber, which is endemic to southwest Europe and northwest Africa. Cork is composed of suberin, a hydrophobic substance.