Anti-pollution mask. The 3M 9004GV is composed of three layers of filters. The outermost layer filters out the largest dust particles. The innermost layer preserves the respirator S shape and the middle layer is composed of electrostatic filter media. Grey color of the mask does not allow the mask to get dirty easily outdoors. These 3 layers helps in purifying the polluted air by upto 95 percent. The cool flow valve makes it more comfortable while using it for long hours and warm or hot conditions.