The filter material is made of gradually dense structure glass fiber. The fiber structure density increases from the air inlet side to the air outlet side. This structure can ensure that dust particles are blocked at a deeper level, thereby increasing the dust holding capacity. Due to the low compressibility of the material, the filter material will not be squeezed when the air is impacted, so that the layers of different density can effectively contain the dust. The filter material is green and white, and the green side is the windward side of the air.