LaserCanvas
Acrylic: cast vs extruded, and why clear beats diodes
Use cast acrylic for engraving — it frosts to a bright white — and either type for cutting, where a CO2 gives a polished, flame-clear edge in one pass. A diode laser cannot cut clear acrylic at all, because blue light passes straight through it. Dark or specially tinted acrylic works on a diode.
Cast and extruded are different materials
They look identical on the shelf and behave differently under a laser. Cast acrylic is poured and cured in sheets; extruded is pushed through a die. The manufacturing difference changes the molecular structure enough to matter.
| Cast (GS / PMMA cast) | Extruded (XT) | |
|---|---|---|
| Engraving | Frosts bright white — high contrast | Engraves nearly clear; low contrast, looks smudged |
| Cutting | Clean, slightly matt edge | Polished, glass-clear edge |
| Cost | Higher | Lower |
| Thickness tolerance | Variable — measure it | More consistent |
| Tendency to melt | Less | More — softens and can re-weld behind the cut |
For most work: cast for anything engraved, extruded when the edge finish is the point and there is no engraving.
Clear acrylic and diode lasers do not mix
This is the most common disappointment in hobby laser cutting. A diode emits around 450 nm — blue light. Clear acrylic is transparent at that wavelength, so the beam passes through and deposits almost no energy. It is not a power problem, and a bigger diode will not fix it.
- CO2 at 10,600 nm is absorbed strongly by acrylic of any colour. This is what acrylic is usually cut with.
- Diode on dark or opaque acrylic works, because the pigment absorbs blue.
- Diode on clear acrylic does nothing useful. Painting the surface or applying an absorbing coating is a workaround for marking, not for cutting.
Getting the polished edge
The flame-polished edge is acrylic’s party trick: cut at the right settings and the edge comes out glass-clear with no sanding. It comes from the material melting cleanly rather than burning.
- One pass, not several. Multiple passes re-melt the edge and cloud it. Find the power and speed that cuts through in one.
- Slower and lower beats faster and hotter — a steady melt rather than a violent burn.
- Less air assist than you would use for wood. Strong air cools the melt and frosts the edge; acrylic does not need air to prevent flame the way wood does.
- Leave the protective film on the top face while cutting to avoid surface scuffing, and remove it from the bottom face so it does not fuse into the edge.
Safety: acrylic is fine, its neighbours are not
Acrylic (PMMA) cuts to carbon dioxide, water and methyl methacrylate vapour. It smells sweet and needs extraction like anything else, but it is not in the dangerous category. Two things it is regularly confused with are:
- Polycarbonate (Lexan) — looks the same, cuts badly, goes yellow and brittle at the edge, and is not worth attempting.
- PVC / vinyl — releases hydrogen chloride, which corrodes the machine and is genuinely harmful. Never cut it.
Common questions
Why will my diode laser not cut clear acrylic?
Because clear acrylic is transparent at the diode wavelength of roughly 450 nm, so the beam passes through without depositing energy. No amount of extra power changes that. Use dark or laser-tinted acrylic on a diode, or cut clear acrylic with a CO2, which acrylic absorbs strongly.
Which acrylic engraves white?
Cast acrylic. The engraved surface frosts to a bright opaque white that contrasts strongly with the sheet. Extruded acrylic engraves nearly clear and looks smudged rather than marked, which is why cast is the choice for anything with engraved detail.
How do I get a flame-polished edge?
Cut through in a single pass at a lower power and speed rather than several fast passes, and reduce or turn off air assist. The clear edge comes from the acrylic melting evenly; extra passes re-melt and cloud it, and strong airflow chills the melt into a frosted finish.
Can I cut polycarbonate instead?
It is a poor substitute. Polycarbonate absorbs badly at CO2 wavelengths, discolours yellow at the edge, and tends to char rather than melt cleanly. It is not in the same hazard class as PVC, but there is no good reason to choose it for laser work.