a controllable length conveyor suitable for use in a packaging machine comprises a pair of conveyor belts which are continuously driven in a given direction at a selected speed . the conveyor belts are mounted on a reciprocable frame and are arranged such that the product being conveyed resides between the belts and a run of each belt firmly engages and transports the product . the belt runs engaging the product can be made to extend and retract in correspondence with the product reaching a succeeding stage of packaging such as sealing .