Dimension: 23" Lx 12.25"W x 2"H, PPI: 30 green medium.The open cell sponge has a much larger inner surface area for filtration capacity..This filter pad can be cut to fit and used as a pre-filter for any aquarium or pond filter, sump, wet/dry, canister, power filter etc. or your HMF DIY project..The reticulated structure also provides better flow rate of water and less chance of clog..The size of pores is measure in pores per inch (PPI). The sponge with higher PPI has more pores in it. More pores means larger filtration capacity but with less water flow through rate and needs to be cleaned more often. It is recommended to use combination of sponge with difference PPI to get the best result.