... metal case 1,CE,SNR:27db,33db 2,smooth surface by anti-pollution treatment 3,wearing health,safety,rebound Ear plug with metal case ... , good flexibility, foam products even , uniform structure, smooth surface withoutadhesive, noise effective,SNR:33DB, This earplug can be washed ... discomfort. Flexibility can not be too small to close contact with the externalear canal, noise effect will be reduced. ...