Sponge air filters of great efficiency made of flexible expanded polyurethane with polyester base, grid. They are made up of two sponge layers; a finer one of light blue color with 60 PPI porosity and one opener of black color with 30 pp porosity The fine layer only filters the smallest particles, maintaining its characteristics longer, since it does not come into contact with the greatest particles, that haven’t surpassed the pre-filtration thanks to the main layer The external surface is waved. It offers a greater entrance of the air flow, retaining a 50% more of dust particles. The efficiency of the filter fulfills the European EN779 of G3-G4 degree rules: more than 90% of ponderal efficiency and more than 50% with 1 micron particles. It is possible to partially restore the filter by washing it and drying it.