Fireproof safes are constructed out of a variety of non-flammable materials. Fireproof can be a bit of misnomer, as nearly every substance will burn if exposed to enough heat. However, safes are referred to as being fireproof rather than fire-resistant because they will withstand the hottest temperatures reached in most residential or office fires. Fireproof safes receive a UL rating based on the length of time they can withstand a fire and the maximum temperatures that can be withstood without damage to the contents inside.
Vermiculite and perlite are two of the most frequently used ingredients in fireproof materials such as doors, cabinets, and safes. Both materials are lightweight, inorganic, inert, and fire-resistant. The two materials are often mixed together to form a fireproof insulation materials that can be used in a variety of ways. Perlite and vermiculite are used throughout the world for their resistance to fire.
Downsides to Fireproofing
Used as fireproof insulation, most materials will lose their effectiveness over time. Fireproof insulation products that are described as oven-baked, oven-dried, or wet take advantage of free-floating moisture in the materials that provides much of its fire resistance. Over time, this moisture will be lost through evaporation and the effectiveness of the insulation as a fireproof material will be lost. There are some safes that are manufactured using a proprietary material that doesn't use free-floating moisture so they will remain effective and fireproof for many years.