Most fire safes are built using one of four construction methods: insulation/fireboard, reinforced fireboard, composite, and composite fire-clad. The composite fire-cladding method is the only construction method that results in a safe that provides substantial protection from both fire and burglary attacks.
The vast majority of fire safes are constructed using one of the low-cost fireboard methods. While fireboard-based safes do provide some fire protection, they are a substantially inferior fire safe that also offers little to no burglary protection. You will never find fireboard or insulating liners in a commercial or high- rated fire safe, simply because they do not work for any substantial length of time.
Because fireboard (aka drywall, fire liner, ceramic fire liner, fiberboard) safes are cheap to manufacture and ship, heavy price markups make them extremely popular among the safe-selling community. Externally, a poorly constructed fire safe is nearly indistinguishable from a well-built safe. It's simply a matter of good marketing hype to convince the customer that one is every bit as good as the other.
For example...Some underhanded manufactures will list the specification ratings of the insulating material used within a safe, allowing the buyer to assume this is the actual fire rating of the safe. In truth, however, the material rating has little bearing on the safe's ability to protect against fire. A UL-listed fire liner' rating of 1½ hours, for instance, just refers to the UL rating of the fireboard panels within the safe and in no way means the safe is UL rated to keep the safes contents below flash point for that stated amount of time. Also, many of the manufacturers will test the safes in their own "labs" rather than having an independent lab perform the tests (preferably UL labs). The customer is left to trust that the quoted fire times are truthful...they quite often are not.
Fireboard-based fire safes do offer some advantages. Because of the low expense to build, some can be highly affordable. Fireboard safes are also significantly lighter, which allows for self-installation. But if the safe fails to actually protect the valuables within, it's functioning as a glorified utility cabinet rather than a true safe. Entrusting your precious belongings to one of these false safes can prove worse than having no safe, as it provides the criminal with an easy opening cabinet where all the cherished household treasures are stored.
Composite-cladded fire safes, on the other hand are heavy, harder to install, and not cheap. But they perform their primary function exceptionally well by protecting your valuables from all harm.