Vaults are made of concrete, plastic or metal. Unlike a burial liner, which only covers the top and sides of the coffin, a vault completely encloses a coffin. Burial vaults are primarily used to keep the weight of the ground from crushing a buried coffin, and also to keep the ground above from sinking in. Manufacturers also state that their vaults can be sealed to keep water and other elements out. In many cases, cemeteries require either a vault or liner to keep the ground over grave sites from sinking in. This gives the ground a neat and even appearance, and helps reduce the chance of a person tripping on sunken ground.
Contrary to popular belief, regardless of whether or not the body is embalmed, a vault will not prevent decomposition of the body.
The use of burial liners is typical only in recent American history and is unheard of outside of the United States. The alternative to using a burial liner is to pile the earth up over the grave in order to allow for settling as is the practice in Europe and other parts of the world. For example, in the UK burial liners are never used because the inevitable subsidence of the earth over a grave is not viewed as a major problem: as the ground subsides over a number of years, earth is added to the depression to level it. Green cemeteries and some religions discourage the use of liners as they slow down the return of the body to the earth.