The Russian GP-5 is probably the most mass produced gas mask of all time. It entered production in the early 70s and ended production in the early 90s. The mask is a grey or black latex hood with two circular lenses and a bottom loading filter and exhalation valve.
The mask was issued to low-ranking Soviet Infantry due to its versatility and revolutionary (at the time) design. Later to be replaced by the PMG and PBF gas masks in the late 80s - early 90s.