Process for producing regular porous pearl cellulose with a particle size in the range from 2 to 1,000 m, comprising the steps:. The server is arranged to: receive a request including a URI having a document identifier which identifies both the whole and a part of the document; determine capabilities of the device; and deliver an appropriate portion of the document containing at least the identified part, the portion depending on the capabilities. An upper plenum is defined by a first spacing between the top and middle sheets. A heating rod is provided in the annular heater.