Cast acrylic versus extruded acrylic
Acrylic is produced in two basic versions, cast and extruded. Cast acrylic is produced by mixing the acrylic liquid ingredients in molds. For acrylic plates between two glass plates. A chemical process in the mold create a homogeneous material with equivalent properties in all directions. In contrast, extruded acrylic is produced by continuously pushing acrylic mass through a form, while the chemical process takes place. Extruded acrylic is therefore heterogeneous, with properties which vary depending on the direction. We call it the extrusion direction for acrylic sheets. Cast acrylic is usually regarded as a better quality than extruded acrylic even though it is in fact two different materials with the advantages and disadvantages.The various production methods provide some small but important differences:
Cast acrylic is more resistant to the same solvents.
When laser cutting extruded acrylic , there will come a burr on one side of the part. On the cast acrylic there is almost no burrs. The edges on extruded acrylic parts can look a bit different depending on the direction of the acrylic extrusion.
The Laser engraving will on extruded acrylic look matt gray. On the cast acrylic will look matt white.
Heat bending and thermoforming
A sheet of extruded acrylic can, because of the acrylic extrusion direction, behave differently depending on the bending direction relatively to the extrusion. With cast acrylic, it makes no difference.
When cast colored acrylic is heated for thermoforming or heat bending the color can change. Matt-colored surfaces can become clear and clear surfaces can become matt. In addition, the shade of color can change. Cast acrylic is harder to bend / shape.
Sheets of cast acrylic vary more in thickness. A cast 3 mm acrylic sheet vary +/- 15%. While an extruded sheet only vary +/- 5%. The dispersion within the tolerance also seems to be less on extruded sheets.
The high tolerance on cast acrylic sheets often comes as a surprise to designers, with many construction errors to follow.
Cast acrylic it more scrats resistant than extruded acrylic.
Cast acrylic is harder to flame polish.
Cast acrylic is produced in a many different color and thicknesses. The color selection is more more limited for extruded acrylic. If one order a special color from a supplier, it will in most cases be cast acrylic.
There is more tension in extruded acrylic.