Cast and Extruded Perspex, what's the difference?

Cast PERSPEX™ is the original cell cast product first produced over 60 years ago. It offers better optical properties and craze resistance than extruded sheet and hence is often the choice for applications requiring critical visual performance.

Technically:

In this process the monomer, Methyl Methacrylate, is polymerised in a bulk process. The liquid MMA (looks like water) is first made into a 'syrup' by heating it up in a vessel, adding a little initiator to get the polymerisation reaction going then cooling when enough polymer as formed to increase the viscosity of the liquid to a syrupy state. To this other additives are added, UV absorbers etc.

The syrup is then poured into a cell made of 2 glass plates with a gasket around the edges and placed in an oven to go solid. The syrup helps reduce leaks etc when filling the cell. The Perspex sheet is then split off from the glass.

This grade of Perspex is usually referred to as Cast Perspex or Cast Acrylic sheet. As its made by the bulk polymerisation route the chains of the polymer are longer and the sheet has much better properties than extruded sheet.

Extruded PERSPEX™ is ideal for general glazing applications that don't require optically perfect properties.

Technically:

In this method the MMA is first polymerised into beads in water to make a PMMA moulding powder. This is used in extrusion + injection moulding. These powders are added to an extruder where they are melted and then extruded and passed through rollers to make a flat sheet.

Extruded sheet tend to have shorter polymer chains than cast sheet plus some of the chains are forced into the direction of extrusion unlike cast acrylic where they are mixed up.