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There is an important group of media materials that are not fabrics in the normally accepted sense of the word, because they are mostly not flexible, but they are made in similar ways, and serve a similar purpose, so they are included here. These are
the sheets and tubes made from bonded components: fibres and granules of natural and synthetic materials. They are mainly only coarsely porous, because it is much more difficult to form very finely granular solids into useful shapes, but some fibre
based materials are capable of very fine cut-off points. An important feature of this group of media is the proportion of inorganic materials that it contains, although polymeric materials are also highly featured.

These media are made by the aggregation of small particles (granules or fibres) of the basic material into useful shapes, either between rolls or in a mould. The aggregate is dosed with a bonding resin and then heated to a temperature where the resin melts and holds the mass of granules or fibres in the required shape. Alternatively, the aggregate is heated to a temperature close to the melting point of the material, under pressure, so that there is localized melting at the points of contact among the particles (and any binder used in the aggregation is driven off or incinerated).

This bonding or sintering process confers an element of rigidity upon the resulting materials, so that they are used, for filtration purposes, either as sheets (including sheets cut into appropriately shaped pieces), or as tubes (open ended or closed
at one end), shown in Figure 2.5. Some of the materials, especially the plastic ones, and in relatively thin sheets, are flexible enough to be rolled up, as can be seen in Figure 2.6 . This is a very useful group of media, with the inorganic nature of some
of the materials enabling their use at quite high temperatures.

These media are made from granules of plastic and metals, and from fibres of plastic, metals, glass and carbon. They are also made by the laying down of meltspun polymeric fibres or filaments onto a rotating perforated core, so as to create a cylindrical filter cartridge.

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