Dumpsters are cut, formed, and welded up from 16 gauge 25-35% recycled steel. Empty dumpsters weigh about nine pounds. When you get a chance to pick one up you will be impressed with its mass. The lid tiles are milled from a wood/plastic composite material that is made from plastic bags and sawdust that would otherwise go to a dump somewhere.
Go see them via Desktop Dumpsters, Mini Steel Art Dumpsters by Ryan Christensen.