There are 3 types of folding methods.  There is the half or mid fold, tranquil hinge, and the breakaway.  There 3 are other styles of folding methods but these are the most widely used.  Folding mechanisms may incur more cost and weight.  One system found on folders such as Montague Bikes utilizes the seat tube as a pivot point for the frame to fold. This system uses a tube within a tube design to give the bike more torsional stiffness. It preserves the structural integrity of the diamond frame. This system is operated by a single quick release found along the top tube of the folding bike.