PPI means: Number of filter sponge pores per unit area At the same time the number of pores also determines the pore size of the filter sponge. The larger the number of pores the smaller the pores. The smaller the number of pores the larger the pores Product Name: proof filtering sponge Application: filter of equipment cabinet server filter of desktop computer DIY filter of digital home appliance of lighting equipment Features: high temperature resistance high elastic shock absorption ventilation and four hazards durable and recyclable material Specification: length 2 meters width 1 meter thickness 3millimeter