This type of foam is produced primarily for use in filtration systems. In order to create a uniform open cell material for such a technical use, the pores of the foam are opened up by means of a special process called reticulation. This additional step in its production makes this version of PU foam more expensive than customary padding or cushion foams. The designation “PPI” (pores per inch) refers to the number (density) of pores in a foam. The given number of pores per inch (25.4 mm) can deviate by plus or minus 5 pores. The version with the finest, and thereby largest number of pores, is the PPI 60. This foam brings to mind the foam found in mattress cores while the courser versions are more similar to carpet foam.
In addition to being used as filter material, the PPI 10 to 30 versions of this foam also serve in architectural model making as a means for representing walls, trees or bushes. When dyed, this foam can be used well in combination with sponge rubber balls.
Our tip: a whole other area of utility for PU foam is in the refrigerator, where it can be used as an underlying layer in the vegetable compartment. It can serve there to hinder bruising or denting of sensitive fruits or vegetables. It also improves air circulation thereby guarding against the development of mould and allowing food to stay fresh longer.
Treatment: These foams can be cut using a blade or shears. Colouring is done by submerging it in poster paint or toning pigment. In the process, and depending on the degree of thinning of the paint, the pores of a fine pored foam will clog up unless it is wrung out as a final step (disposable latex gloves).