Abstract: A binder for sheets of paper comprises a bendable cover and a binding system secured centrally of the cover. The binding system has a one piece plastic construction comprising a base portion with first and second bosses formed from and located to either side of the base portion. The first boss has a plurality of spaced apart recesses and the second boss has a plurality of spaced apart posts which lock into the recesses of the first boss when the binder is folded upon itself in a binding position. Also provided are first and second sets of ribs again formed from the base between the first and second bosses. The ribs are hollow and are open from beneath to ease the bending of the binding system when the binder is folded to the binding position.