a heavy - duty flat wiper blade assembly has a wiper element and an extruded metallic frame . the frame has a bottom channel with a slot traversing its length in which the wiper element is maintained . the wiper element extends through the slot and outwardly from the bottom channel to make contact with a surface to be wiped . the frame has a closed upper channel that may include a fluid inlet opening for receiving wiper fluid into the channel and a fluid outlet opening for discharging the wiper fluid from the upper channel onto a surface to be wiped .