No. I have no idea how my numbers proved that. Small amounts of air heat faster than large amounts of air, so the protection would have to be greater. Yet in those cases, cement filled safes are being used. You gave an example of a very large cube, which would heat much more slowly due to the huge volume of air within. It's using ceramic, although most still do not. Regardless, we're still talking about safes and not vaults, and we still haven't been able to find an example of a safe with a UL rating using ceramics as its primary insulation. Actually both materials, ceramics and cement/concrete/composite/etc., transfer heat. I know this because my home oven is surrounded with ceramic inuslation, and yet it still gets warm on the outside when heating from the inside. All man made materials will transfer heat. I have found several materials used, including ceramics and even foam. However, the outer chamber is what does the heavy lifting, and that has always been cement. The outer chamber (the safe itself) is protecting against the 1700 and 1800 degree heat for 1, 2, or 4 hours, while keeping the interior of that chamber at 350 degrees or less. The inner chamber (the ceramic or foam lined container) is protecting against the 350 degree interior temperature of the outer safe, while keeping its interior at 125 degrees or less. There have been several banks that have burned down in the last hundred or so years. Can you point me to one where the cement vault failed to protect its contents? You may not be aware, but NFPA and UL are two entirely different organizations. The "NFPA-75" that you mention has nothing to do with UL. You can read the 1999 version of the NFPA standard here: http://www.minhbao.vn/userfiles/file/A_NFPA75.pdf Just giving it a quick glance, and it looks like you can use any material, so long as by building code it gives a "fire rating". Since it doesn't give a specific list of approved materials, I'm assuming your ceramics would work along with gypsum board, cinder block, brick, or concrete. I'm going to have to research the ceramic products you pointed to in those links to see if a) they really do carry a UL rating, and b) if so, which standard is being used for testing. Then I can comment further on the aspect of its rating, as issued by UL (if any). Edited: Houston, we have a problem. Your ceramic vault panels you linked to made by Firelock don't appear to be UL rated in any way, shape or form. The panels appear to meet your NPFA standards, and that's it. The door to the room is in fact a UL rated vault door, and it uses a secondary door to meet the media storage requirements. By the way, the door shown on their site is a cement filled Schwab. The Veritrust site does mention UL testing of their panels one time, but then goes on to explain on site modification of the vault during the assembly process. Since UL can not guarantee that these modifications are made in the same fashion as they were during the testing process, they will usually not certify the product without having an onsite inspection of the finished product. There's a big jump in UL's involvement in ratings involving theft. Most gun safes have an RSC rating, which is a BS rating, and also isn't worth the the sticker it's printed on. It does look good in sales literature though. A B rate safe is a safe using up to a 1/2" plate door, and up to a 1/4" plate body. Technically all safes are B rated at a minimum, although a true B rate safe is considered to use the full thickness. The first burglary rating UL has above the RSC is the TL-15 (heavy plate safes). Using A36 steel, your gun safe would have to have a 1" plate body, and 1.5" plate door to get this type of rating.