Reticulated Polyester Foam. This is what Pipercross used to use in their air filters and spray it with silicon to 'catch' the bits. To get the egg box effect, foam is put between two rollers with 'feet' and depending on how much it is compressed when the blade glides between the two rollers depends on how much off an egg box effect you get. The thing is would you want to wash your car with this?
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PS I designed the sponge that used to go into the Kiddicraft Vac that many of you will remember from your childhood