The flask is made from high quality food grade 304 stainless steel. The flasks main body is a full 5mm thick, about twice as thick as an average flask. This means that it will not easily puncture , dent or ding and has a good weight to it. The joints at the top and bottom are welded with a high powered laser which ensures that the flask will not separate or leak. Finally the flask is leak tested using a proprietary system that submerges the flask under water and injects air into it while a machine scans for bubbles; If no bubbles appear in the water the flask is air-tight.