5 layer filter material for protective mask First, carbon sheet. The second layer is thick and dustproof. Layer 3, spit prevention, layer 4, fine fibers, air purification, Shutterstock .eps vector - 5 layer filter material for protective mask First, carbon sheet. The second layer is thick and dustproof. Layer 3, spit prevention, layer 4, fine fibers, air purification, - ID: 1663984471