All Peli cases are made of a high impact structural copolymer resin and use O ring sealing technology to make them watertight, airtight, and unbreakable in normal use. (Normal to you might be different from normal to us. They probably wouldn't survive being driven over by a 40 tonne main battle tank.) There's an automatic pressure purge valve to cope with the problem of significant changes in atmospheric pressure, i.e. being unable to open the lid because of the pressure difference. All hinges use stainless steel rods.