Corks are a material used for bottle stoppers. Corks are made from the bark of cork oak trees used to close amphoras, barrels and glass bottles. Cork's elasticity combined with its near-impermeability makes it suitable as a material for bottle stoppers. Cork is also used in rocket technology due to its fire resistance. It can also be used as bricks for the outer wall of a house. It also has low heat conductivity and is used as an insulating material.