A burial vault is a case that is used to hold a casket for burial. No matter how much money you spend on your loved ones casket it will eventually decay and break down; the burial vault prevents it from collapsing under the weight of the dirt above it. A burial vault can be purchased from a number of materials, plastic, concrete, or various metals.
Many cemeteries will insist that a burial vault of some type or at the very least a casket liner be purchased to prevent the ground above from sinking when the casket below decays. A casket liner is significantly less expensive than a vault as it covers the sides and top of the casket but leaves the bottom exposed, whereas the vault completely encases the casket. Some vaults actually boast being water proof, and air tight.
In cemeteries that do not insist on vaults they still tend to be fairly popular because the survivors have difficulty with the thought that they spent money on a casket just to have it crush under the weight of the dirt. They have spent X number of dollars on a casket to give their loved one a comfortable eternal rest and cannot imagine the eternal resting place they chose for their loved one being crushed under hundreds of pounds of dirt. When it is stated that way it sounds very dramatic for sure.
There are thousands of other people who choose not to spend the extra money each and every year, surely they have their reasons. If money is a concern, and you have an options to buy a vault, liner, or not buy either, you should not buy either. In the end the same thing will end up happening. Even in cases where a vault is purchased and it is of the highest quality, air tight and water proof, eventually the body will decay, how long it takes depends only on the skill level of the embalmer and the strength of the chemicals used. No matter how high quality the vault is, it will not prevent the body and its casket from eventually breaking down. Wood, like the human body is a natural substance and therefore has only a limited shelf life so to speak.
If you are considering buying a burial vault because you have been given the impression that it will prevent your loved ones casket from ever breaking down, and their body from ever decaying, you should reconsider. Unfortunately there is simply nothing on the market today that can offer that type of protection. A burial vault will increase the length of time that the casket will remain intact but that is all. If you are considering buying a burial vault because the cemetery is insisting on one, you should ask them about whether or not a casket line would be just as good to meet their needs. Going this route can save you a considerable amount of money while still preventing the dirt from sinking.