As clearly shown in these photographs taken using a microscope, the cotton filter (H&M) is made of extremely coarse yarns while the polyester filter (SUPERCOMPETITION) is made of much finer yarns sized to the micron. Thanks to this special design, polyester fabrics guarantee more efficient filtrationand excellent air permeability as all our tests have shown. Nonetheless it is to be pointed out that the results obtained by testing cotton fabrics have not been 100% reproducible and this is due to the weak and yielding texture of the cotton gauze. However the following results are the best results we obtained. As to polyester fabrics, results have always been 100% reproducible and accurate. Air permeability Diagram N° l shows fabric air permeability at 20mm of H2O. Polyester shows higher values than cotton: 5,050 liter/m2s versus 4,900 liter/m2s. Filtration efficiency Diagram N° 2 shows the filtration efficiency of both fabrics. It is to be pointed out that tests have been carried out using water instead of air. And this gives a remarkable advantage to cotton whose fibers showed a higher degree of filtration efficiency thanks to their swelling. However polyester showed the best results: 93.13% of 100-micron particles have been sieved out versus 76.42% of 100-micron particles trapped by cotton. Compatible with: - Buell: 1125 C/CR_M