Filter foam is a foam with precisely defined cell size, i.e. a defined number of cells per unit length. It is expressed in ppi [pores per inch]. A 10 ppi foam, for instance, has larger pores than an 80 ppi foam.
An accessory device will be fitted to the foam machine to produce filter foams, ensuring not only that the required cell size can be reproduced but also allowing the production of cells that would otherwise not be possible. This will allow producing almost the entire possible range of cell sizes, i.e. from 3 to 30 cells / cm. The additional reticulation for these types of foams allows virtually 100% open-celled structures. This will reduce the through-flow resistance to gases and fluids to a minimum.
Filter foam is used in