Check the listing for details. Filstar Progressive Micro-Filter 2pack Dual Layer Fine/Extra Fine Fits All. Condition: New, Made in United States. Listed at 9.77 USD. API Rena Filstar XP Dual-density Microfilter pads are the final stage in the mechanical filtration of the aquarium with the API and Rena Filstar external canister filters. These will remove the smallest of particulate matter and are used to "polish' the water. These dual-layer pads will last twice as long as the standard micro-filter. Included with the API XL and Rena Filstar 4 they can also be used with all Filstar filters including Filstar S, M, L and Rena Filstar 1,2,3. Each pad is two layers with coarse density fibers in one layer for trapping larger particles and a finer density which traps the smallest debris. This design allows the larger particles to be trapped in the first layer while the second layer traps the remaining finer particles.