Extrusion for glasses to which the usual processes of casting, blowing or drawing are difficult to apply. This is true for glasses with a narrow working range (short glasses), for glasses which strongly tend to crystallize and for glasses with a very high softening point.
Due to the extrusion pressure, the working range is enlarged to higher viscosities, the manufacturing process is shifted into a range of lower crystallization rates and the lower working temperature can be controlled in a more convenient way.
Extrusion could be applied to conventional glasses, if products with non-circular cross sections are to be manufactured.