Are 120 volt heating products more efficient than 240 volt?

No. Both floor heating systems have the same efficiency and produce the same amount of power: 12 watts per square foot. The only difference is that 240 volt mats pull half the amperage (current) of 120 volt models, which means a single thermostat can control up to 300 sq ft of 240 volt heating elements while 120 volt systems are limited to 150 sq ft. The only instance in which 240 volt is recommended for rooms smaller than 150 sq ft is when there is already an available 240 volt circuit in the room.