The law does not require the use of an outer burial container, commonly known as a vault or grave liner, but cemeteries may require them to keep the ground from settling.””The weight of the earth on top of the casket, plus heavy cemetery maintenance equipment running over it, can cause the casket to collapse over time. Without an outer burial container or vault, the soil over the grave would sink, harming the appearance of the cemetery grounds.

There is a simple yet significant difference between vaults and grave liners. Grave liners are intended solely for the purpose of supporting the soil. They add little protection from outside elements such as water and dirt to the casket.  Vaults on the other hand are designed to help protect the casket as well as to support the soil above the casket and vault. 

One type of outer burial container is a grave liner. Grave liners are typically made of concrete. This type of outer burial container may totally enclose the casket on all sides, top, and bottom, or it may be made to only protect the sides and top of the casket.  

Burial vaults, on the other hand, will always have a bottom and the structure will always completely enclose the entire casket. Most concrete burial vaults also have some kind of plastic interior liner that forms a seal. Burial vaults are available in a range of styles and can be made from basic, mid-range, or extremely high-quality materials. The interior plastic liner in burial vaults serves as a kind of barrier between the casket and the elements.