What is the difference between cast and extruded acrylic?

Both are acrylic, the plastic called PMMA. Cast sheet, often cell-cast, engraves with a frosted look and usually cuts with a cleaner edge on a CO2 laser. Extruded sheet is more uniform in thickness, melts more readily, and engraves clearer and gummier. Buy cast when the frosted mark or a polished-looking edge is the product. Buy extruded when you are cutting simple shapes and the listing is honest about which one it is.

Can a diode laser cut clear acrylic?

Do not plan on it. A blue diode beam, often near 445 nm, mostly passes through clear acrylic instead of being absorbed. The beam can mark the bed underneath, which is a failed cut and a fire risk. Dark, opaque acrylic is the realistic diode material. Clear, and many light colors, are CO2 work.

Is polycarbonate the same as acrylic?

No. Polycarbonate, sometimes sold under brand names people use for unbreakable glazing, cuts poorly, discolors, and does not belong in a hobby laser. The word plexiglass on a listing does not tell you cast from extruded, and it does not prove the sheet is acrylic at all. The label should say acrylic or PMMA, and whether it is cast or extruded.

Should the protective film stay on during a cut?

Paper masking can stay on to protect the face from flare. A plastic film should come off unless the seller states it is safe to leave on. Some films are polyethylene and some are materials you should not laser, including vinyl. If you cannot tell, peel it. A paper-masked sheet avoids the question.

Why did the edge come out frosted or ridged?

Cast acrylic can flame-polish on a CO2 cut when power, speed, and air assist are in balance. Too much air frosts the edge. Too little lets flame scar it. Extruded acrylic is more likely to show a melt ridge no matter what you do. Tune on a scrap of the same sheet. A diode will not give you that polished clear edge, because it is the wrong tool for clear stock.

Acrylic for laser cutting and engraving

Acrylic is the plastic hobby lasers are supposed to like, and it is also the plastic people confuse with three others that should never see a beam. Get the name right first. Acrylic means PMMA. It is not polycarbonate, not PVC, not PET, and not “a clear sheet from the hardware aisle” until the label says so. Cast and extruded are both acrylic, and they do not engrave the same way. A diode and a CO2 do not treat clear sheet the same way either. Most beginner disappointment is one of those two mix-ups.

Cast versus extruded

Cast acrylic is made in a cell, and the sheet can vary a little in thickness. That variation is a nuisance for a precision slot and a clue that you might have cast stock. When a CO2 laser engraves it, the mark frosts to a pale, readable white. Cuts, with air assist and a sensible speed, often come off with an edge that looks close to polished. Awards, edge-lit signs, and anything where the engraving is the design want cast.

Extruded acrylic is pushed through a die. Thickness is more consistent, which is nice for stacks of simple parts. It melts more. An engraving looks clearer, sometimes almost invisible, and the cut edge can carry a ridge of melt. It is a fair choice for a simple cut shape when the listing is cheap and correctly labeled. It is a poor choice for a photo portrait you wanted to look frosted.

If the listing says only “acrylic,” ask which process. Craft-store blanks are often extruded, or they are not acrylic. A plastics supplier is more likely to print cast or extruded on the skid. There is no home tap test we are willing to call reliable. The practical check, once you have a CO2 and a scrap, is the engraving itself: frosted and crisp leans cast, clear and gummy leans extruded. Label your own offcuts so the next job starts from the right pile.

Colors and diode limits

A CO2 beam is absorbed by clear acrylic and by most colors. Mirror-finish sheet is usually a film on the back. If you cannot name that film, peel it. Do not assume it is acrylic.

Black cast acrylic is the honest diode acrylic, because the pigment absorbs blue light. A see-through product wants a CO2. Test one small piece of a color before you buy a pack.

Prefer sheet colored in the plastic itself. A sprayed coating might be fine and it might be a chlorine plastic. The never-laser list applies to coatings too.

Thickness and edges

Hobby CO2 machines commonly cut around 3 millimeter sheet, often sold as one-eighth inch, in one pass when the tube, focus, and air are in decent shape. Thicker sheet, around 6 millimeters, wants more power, a slower speed, or more than one pass, and the edge quality usually drops. A diode cutting dark acrylic is slower again. Extra passes increase melt and can taper the edge. If the part must fit a slot, cut a test and measure it. The drawing’s hole is not the finished hole. Kerf removes material, and melt can put some of it back.

A good CO2 cut on cast acrylic is often glossy enough without chasing a glass edge. Running very hot is how a flare starts. Use air assist, stay in the room, and accept a slightly matte edge. Keep sheet flat so focus does not drift, and support cuts on a honeycomb so the back does not flash against the table.

Masking film

Most acrylic arrives with a film or a paper mask so the face survives shipping. Paper is the easy case. Leave it on for a cut if you want the face protected from flakes, then peel it. If the paper chars into the artwork, you had too much heat in that area, or the paper was not a light mask. Engrave a sample.

Plastic film is the case that hurts machines. Many films are fine to peel and throw away. Some are vinyl or another plastic that releases nasty fumes if the laser cuts them. The safe workshop habit is dull: peel plastic film off before the job unless the seller has said, in writing, that this film is meant to be lasered. “It came on the sheet” is not that sentence. Paper-masked acrylic costs a little more sometimes and removes the guess. If you have already peeled one corner and the film smells sharp or stretches like vinyl tape, stop and peel the rest, and do not laser the crumbs.

Plastics that are not acrylic

Polycarbonate yellows, melts badly, and is a fume problem. It is sold as unbreakable window plastic and as a 3D-printer bed. It is not a laser acrylic. PVC and vinyl are the classic never, including some “clear craft plastic” and some colored sheets in the sign aisle. ABS is a no. PET and PETG are not acrylic either. They are common in packaging and in printer filament, and they are not the sheet this page is about. HDPE and polypropylene melt, can catch fire, and are the cloudy cutting boards of the plastics world. Do not test them beside the acrylic just because they are in the same scrap bin.

If a piece has a recycling mark, read it. Mark 3 is PVC and does not go in the machine. Marks are not always present, and a missing mark is not a yes. The rule from the materials guide is the one to keep: if you cannot name the polymer, it does not get a test pulse. A burn test to “see what it is” is you doing the dangerous thing in order to decide whether to do the dangerous thing.

When the job is a keychain or a small sign, buy the sheet labeled cast or extruded, in a color your machine can actually absorb, and cut one before you cut twenty. Diodes start with black cast. CO2 machines can start with clear cast if the polished edge is the point. The machine guide is the place to decide which of those machines you are shopping for. Acrylic will not talk you into the other one.

Acrylic to look up

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Amazon search Cast acrylic sheet Search words: cast acrylic sheet Sponsored link. Opens in a new tab.
Choose cast when you want a frosted engraving or a cleaner CO2 cut edge. The listing should say cast or cell-cast, not only acrylic.
Amazon search Extruded acrylic sheet Search words: extruded acrylic sheet Sponsored link. Opens in a new tab.
A cheaper, more uniform sheet for simple cuts. Expect more melt and a less frosty engrave. Do not buy it by accident when you wanted cast.
Amazon search Black cast acrylic sheet Search words: black cast acrylic sheet Sponsored link. Opens in a new tab.
The practical diode color, and a normal CO2 color too. Prefer cast if the listing offers it. Confirm it is solid acrylic, not a painted film on clear.
Amazon search Clear cast acrylic sheet Search words: clear cast acrylic sheet Sponsored link. Opens in a new tab.
Buy this for a CO2. A diode will usually pass through it. Paper-masked clear cast is the straightforward sign-making sheet. Peel unknown plastic film first.