It is essential that the vault door you purchase has a continuous solid steel plate of substantial thickness. Without this base level of steel protection, any vault door can be opened within minutes despite the hoopla of additional advertised protection features. The majority of vault doors on the market tout a plethora of protection features, but virtually all fail miserably in this essential area.
The vault you choose must have at minimum a ½" thick solid steel door.
Steel is very expensive and heavy, vastly increasing the door's build cost and the cost of shipping overseas to the reseller. As a result, nearly all oversea-manufactured vault doors (and even many locally built vault doors) cut these costs by constructing their doors with thin sheet metal wrapped around various forms of drywall to give the appearance of a robust door.
Be highly suspect if the vault manufacturer or reseller doesn't state solid steel or lists "composite" for their door material, as this can be anything from sheet metal wrapped around wood to sheet metal and drywall.
Also be on the lookout for vault sellers that list just 'door thickness' rather than the barrier material type and thickness as this is a recent trick many underhanded vault marketers employ. By listing the total thickness of the vault door including the dial, barrier material, airspace, inner boltwork, etc., the provided figure can sound quite impressive while actually preventing the buyer from obtaining any solid information on how thick the barrier material actually is or what it's made of.