Cast and extruded acrylic are both PMMA (polymethyl methacrylate). Same chemistry. Same basic appearance. But the way they’re manufactured changes how they behave when you cut them, laser them, polish them and form them. For many applications the difference is academic. For others, it’s the difference between a clean result and a ruined sheet.
How They’re Made
Cast acrylic is made by pouring liquid PMMA monomer between two sheets of glass, which is then cured (polymerised) in an oven. The result is a sheet with a high molecular weight, excellent optical clarity and tight colour consistency. It’s a slower, more expensive process but it produces a superior material.
Extruded acrylic is made by pushing PMMA pellets through a heated die, like squeezing toothpaste from a tube. It’s a continuous, faster, cheaper process. The resulting sheet has a lower molecular weight and slightly different physical properties.
Where It Matters
Laser Cutting
This is the biggest practical difference. Cast acrylic laser-cuts beautifully. The laser vaporises the material cleanly, producing a smooth, flame-polished edge that’s virtually clear straight off the machine. This is why every sign maker, trophy manufacturer and laser-cutting workshop specifies cast.
Extruded acrylic doesn’t vaporise as cleanly. The laser tends to melt the edges rather than cut them, producing a gummy, frosted finish that needs post-processing. It can also produce bubbling along the cut line. If you’re planning to laser-cut your acrylic, cast is the only sensible choice.
Edge Polishing
Cast acrylic responds well to flame polishing a quick pass with a hydrogen torch produces a glass-clear edge. Extruded tends to bubble and produce an uneven, pitted surface when flame-polished. Mechanical polishing (sanding and buffing) works on both types, but cast produces a clearer, more consistent result.
Thermoforming
Extruded acrylic has one clear advantage: it thermoforms more easily and at a wider temperature range. It softens more uniformly, which makes it more forgiving in vacuum forming, drape forming and line bending. If your application involves heating and shaping the sheet blister packs, formed displays, curved components extruded can be the better option.
Cast acrylic can be thermoformed, but it has a narrower working temperature window. It needs more precise temperature control to avoid uneven softening.
Thickness Tolerance
Cast acrylic is manufactured to tighter thickness tolerances. A sheet specified as 3mm will typically measure within ±0.2mm of that figure. Extruded sheets can vary by ±10% or more a “3mm” extruded sheet might measure anywhere from 2.7mm to 3.3mm.
This matters for precision applications slotted fittings, layered assemblies, or anything where multiple sheets need to stack or align accurately.
Chemical Resistance
Cast acrylic has better solvent resistance than extruded. It’s less prone to stress crazing from cleaning products, adhesives and environmental chemicals. This makes it more reliable in long-term outdoor installations and environments where cleaning chemicals are used regularly.
Optical Quality
Both types offer excellent clarity, but cast acrylic typically has fewer internal stresses and a more uniform refractive index. In practice, most people can’t tell the difference by looking at the surface. Where it shows up is in applications that transmit light backlit panels, lightboxes, display cases where cast produces a more even, distortion-free illumination.
Cost
Extruded is cheaper. The continuous manufacturing process is faster and more efficient, which translates to a lower price per sheet. For large-volume, non-critical applications (protective coverings, temporary barriers, basic glazing), the cost saving of extruded can be significant.
For anything that involves laser cutting, edge finishing, long-term outdoor exposure or precision fabrication, the premium for cast is worth paying — the material performs better and the end result looks better.
What Does Plastic Sheets Direct Stock?
Plastic Sheets Direct supplies cast acrylic across the full range of clear, coloured, frosted, mirror and fluorescent finishes. Cast is the right choice for the vast majority of applications better laser compatibility, better edge finishing, better long-term performance and tighter dimensional accuracy.
If your project specifically requires extruded acrylic for thermoforming or high-volume budget applications, get in touch and the team can advise.