Laser Cutting Acrylic: Cast vs Extruded, Settings, Safety

Acrylic is the material that makes a laser look like magic: glossy, glass-clear edges with no sanding at all. It is also the material that most often surprises beginners, because two sheets that look identical can behave completely differently. This guide to laser cutting acrylic explains cast versus extruded, what your machine can and cannot cut, how to get polished edges, and how to stay safe while you do it.

Cast vs extruded acrylic

Acrylic (PMMA, sold under names like Perspex and Plexiglas) comes in two main types. They look the same on the shelf but the laser sees them very differently.

Cast acrylic

Cast acrylic is made by pouring liquid acrylic between sheets and letting it set. It is harder and more stable.

Engraves frosty white, giving strong contrast on clear sheet. This is what you want for signs, awards and lit edge panels.
Cuts with a clean, flame-polished edge.
Thickness varies a little across the sheet, so measure before making joints.
Costs more and comes in a huge range of colours.

Extruded acrylic

Extruded acrylic is pushed through rollers. It is cheaper and more consistent in thickness, but softer.

Engraves clear or faint rather than white, so engraving has less contrast.
Cuts with a very glossy edge, but melts more easily and can leave a gummy lip or drips.
Parts can weld back together if the beam lingers on tight corners.
Good for simple cut-out shapes where you do not need engraving.

If your supplier does not say which type a sheet is, ask. When in doubt for engraved work, buy cast.

Can your laser cut acrylic?

This is the first question to answer, because it depends heavily on the type of laser.

CO2 lasers (the common 40 to 150 W tube machines, and machines such as Glowforge and OMTech units) cut clear and coloured acrylic very well. This is the ideal tool.
Diode lasers emit blue light that passes straight through clear acrylic and through many blue and light colours. They can often cut dark, opaque sheets such as black, but slowly and with rougher edges. If you only have a diode laser, test a scrap of the exact colour before buying a stack.
Fibre lasers are made for metal and are not a good choice for cutting acrylic.

Is it really acrylic?

Polycarbonate and some other clear plastics look almost exactly like acrylic. Polycarbonate does not cut cleanly: it burns, turns yellow-brown and produces nasty fumes. PVC sheet is even worse and must never be cut. If a sheet has no label and you cannot confirm it is acrylic, do not put it in the laser. Our list of materials you should never laser cut covers the lookalikes.

Setting up for laser cutting acrylic

Protective film

New sheets come with paper or plastic film on both sides. Leave the paper on when cutting; it protects the surface from smoke and stray reflections. Plastic film can melt into the edge, so many makers peel it off the top before cutting, or before engraving in any case. Some people swap it for low-tack masking paper.

Raise the sheet

The back of the sheet can pick up marks from beam reflections off the honeycomb. Lifting the acrylic on pins or a slatted bed reduces this.

Air assist

Air assist keeps flames down and pushes fumes away. Some makers lower it a little on acrylic because very strong air can cool the edge and make it look slightly frosty. Never cut with it off if your machine depends on it to prevent flare-ups.

Ventilation and fire safety

Acrylic gives off a strong, sweet-smelling vapour as it vaporises. Extraction must be running before you start and should vent outdoors or through a proper filter. Acrylic also burns readily once alight. Stay with the machine, keep a CO2 fire extinguisher nearby, and stop the job immediately if you see a sustained flame rather than a small flicker at the beam.

Settings to start testing

Machines differ, so use these only as starting points. On a 40 to 60 W CO2 laser, 3 mm cast acrylic often cuts somewhere around 5 to 15 mm/s at 70 to 90 percent power in one pass. Thicker sheet needs slower speeds, and 6 mm or more benefits from accurate focus about halfway into the material.

The edge tells you a lot:

Clear and glossy: you are close.
Frosted or striped: usually too fast or too much air assist.
Bubbled or melted lip: too slow or too much power, especially on extruded sheet.
Not through at the bottom: slow down slightly or check focus and lens cleanliness.

Kerf and fit

Acrylic does not compress like wood, so joints must be accurate. A press fit that is fine in plywood can crack acrylic. Our tool uses a starting kerf of 0.12 mm for 3 mm cast acrylic, and you should check it with a laser kerf test on your own machine. For acrylic, aim for a snug slide-in fit rather than a tight press fit, and add a drop of acrylic cement if you need it permanent.

Designing parts for acrylic

Avoid sharp inside corners on parts that will be stressed. A small radius spreads load and reduces cracking.
Keep the order sensible. Engrave first, then cut inner shapes, then outlines.
Reverse-engrave clear sheet. Mirror the design and engrave the back face, then view it through the front for a protected, glossy look.
Use colour layers. Red for cuts, blue for engraving and green for scoring keeps the job easy to set up in LightBurn or your machine's software.

Our laser cut tool can generate signs, photo frames, phone stands and boxes for acrylic. Choose cast acrylic as the material and it applies the matching starting kerf to the joints, and the material guide in the download includes notes for that sheet. If you are turning a logo or photo into a cut-out, the photo to laser file option traces the outline for you.

Common acrylic problems and fixes

Parts melted back into the sheet. Too slow, or the beam paused in corners. Speed up and check that your software is not adding long dwell times.
Cracks near joints or holes. Joints too tight, or parts too close to the edge. Loosen the fit and keep holes at least one material thickness from the edge.
Cloudy engraving on extruded sheet. That is normal. Use cast acrylic for white engraving.
Edge haze after a day or two. Often stress from cleaning with alcohol-based products. Clean acrylic with mild soapy water instead.
Flames during the cut. Check air assist, slow cuts on small parts, and stop if a flame keeps burning.

For other materials worth trying next, see our guide to laser cutting plywood.

Frequently asked questions

Can a diode laser cut clear acrylic?

Generally no. Most diode lasers emit blue light that passes through clear acrylic. Some can cut dark opaque acrylic slowly. A CO2 laser is the right tool for clear sheet.

Should I use cast or extruded acrylic for laser cutting?

Cast acrylic for anything engraved, because it frosts white. Extruded is cheaper and fine for plain cut-out shapes.

Do I remove the protective film before cutting acrylic?

Paper film can usually stay on for cutting. Plastic film is best removed from the top before engraving and often before cutting, as it can melt into the edge.

Are acrylic fumes dangerous?

They are irritating and strong-smelling, so always cut with extraction that vents outside or through a suitable filter. Never cut in a room without ventilation.