Cast vs Extruded Acrylic? What are your overlays made of?

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When you look at the descriptions of our acrylic overlays, you’ll see terms such as Clear Cast Acrylic or Clear Extruded Acrylic.  What is the difference?  Why do we use different types of acrylic?  Is one type better than the other?  What should you look for when purchasing acrylic overlays?

Cast and Extruded acrylic are both PMMA (Poly methy-methlacrylate).  You may know it by a regional or brand name such as perspex, plexiglas or optiplex. The difference is in the process.  Cast and Extruded are named by the way that they are manufactured.

Cast acrylic is premixed and poured into a mold.  This makes a shape with little variance properties in all directions.  It is a homogeneous mix. Extruded acrylic is constantly being pushed through a die (like a caulk gun) while in the process of activating.  This creates a heterogeneous mix with variance in chemical properties along the extrusion direction.

Which is better? That depends upon the purpose, the cost, and the processing technique.  Each has properties that would lead a manufacturer to chose it when it is suited for the product.

I’ll give you a list of properties as they pertain to use for overlays:

 

Close up of character name etching on Robinson Crusoe:Voyage of the Beagle Health Trackers.
Cast Acrylic with etching

Cast:

  • More resistant to solvents
  • More resistant to scratches
  • Laser cuts with a smooth clear edge
  • Engraves white on clear
  • Clear cast acrylic has a more glass like appearance
  • Available in many colors
Extruded Acrylic

Extruded:

  • Available in thinner profile than cast
  • Can have a directional “burr” on the edge that flows with the extrusion direction when cut with a laser
  • Has a lower melt point
  • Easier to shape/bend
  • Easier to flame polish
  • Lower cost
  • Engraves gray on clear

Cast acrylic is our choice for most of our overlays.  While it is more expensive than Extruded acrylic sheet there are several reasons it is our choice.  We believe the way it performs on the laser, and the clarity provided by the casting process produces a better quality product.  In addition the cast has more resistance to scratches and solvents making it a more consumer friendly choice.

In our case, we only use extruded plastic when we need acrylic below 3mm thickness.  It’s a choice based on the lack of common availability of <3mm clear cast acrylic sheet.

When shopping and comparing acrylic products, always make sure you know what type of acrylic sheet is being used.  Make sure you are comparing apples to apples and not apples to oranges.

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