Combined gas and particulate respirator filter for protection against acid gases, the type of BKF (БКФ). It has transparent body and special sorbent that changes color after the saturation. This color change may be used for timely replacement of respirators' filters (like End of Service Life Indicator ESLI). The filter is made, presumably, in the city of Dzerzhinsk, Nizhny Novgorod region (RF).