 Although large compound strings of firecrackers have been constructed since firecrackers were invented, the superstring was greatly popularized by the Pyrotechnics Guild International, whose yearly convention often features a huge superstring consisting of well over a million firecrackers.Superstrings are usually constructed over a rudimentary wooden or metallic structure as a sort of curtain wall.The largest superstring ever constructed was built by the Pyrotechnics Guild International in 2006.