My thoughts, based on this statement from the coppermind is that they’re just huge slabs of aluminum with the fabriel boxes on back being a red herring. What are your guys ideas?
Items can be Soulcast into aluminum.[7] However, aluminum resists attempts to Soulcast it into other essences.[24] Shardblades are unable to cut aluminum through magical means but would be able to cut it physically, like a conventional blade, if the aluminum were thin enough.[25] Aluminum can block spanreed communication, and can prevent Soulcasting from being detected by others.[26] Aluminum cannot be affected by the surges Adhesion or Gravitation.[27] It likely can't be affected by any surge.