Sorry Max, the only really thick heavy stuff I have seen goes back to the laminated plate era of the late 1800's-early 1900's. It did seem a bit strange when I started in the trade that Mosler/Diebold were importing safes for the jewelers market. Then again, they both had the banking industry heavily covered with regional sales and service offices in many larger U.S. cities. Here in the states, we see jewelers safes from all over the world, Kaso from Finland all the way to Lord from Australia. SLS had an office in Philadelphia, which I suppose is how that Gem safe ended up here. And Tom on that H-H-M safe, it is possible the outer door had insulation, but outwardly it was a typical solid steel laminated door. Unfortunately I cannot find the pictures I took of it.