Short answer: Cast acrylic is made by curing liquid acrylic in a mold; extruded acrylic is melted and pushed through a die and rollers. Cast engraves a bright frosty white, machines cleanly, resists crazing, and handles a little more heat (Acrylite cast is rated for 180 °F continuous vs 160 °F for extruded), so it's the choice for engraved signs, awards, and bonded cases. Extruded costs less, holds its thickness about twice as tightly, and bonds faster with solvent cement, so it suits plain panels, covers, and frames.
How cast and extruded acrylic are made
Both are PMMA (polymethyl methacrylate), the same material sold as Plexiglas, Acrylite, Perspex, Optix, and other brands. The difference is the process.
- Cast acrylic starts as a liquid syrup poured between two sheets of glass (cell cast) or onto a moving steel belt (continuous cast) and cured slowly. The long polymer chains end up tangled and evenly arranged, with little built-in stress.
- Extruded acrylic starts as pellets that are melted and pushed through a die, then pressed between polished rollers. It's faster and cheaper to make, but the chains are shorter and get stretched in the direction the sheet travels, which leaves some orientation in the sheet.
Clarity is the same to the eye: makers rate both at 92% light transmission. You can't tell them apart on a shelf. You can tell them apart the moment you engrave, glue, or heat them.
Key facts
- Heat: Acrylite cast is rated for 180 °F (82 °C) continuous service and softens (Vicat) at 239 °F (115 °C); Acrylite Premium extruded is rated for 160 °F (71 °C) and softens at 220 °F (105 °C).
- Forming: cast forms at about 340 to 380 °F (170 to 190 °C); extruded at about 290 to 320 °F (143 to 160 °C).
- Shrinkage when heated: cast typically shrinks about 1.5 to 2%; extruded shrinks up to 3% along the extrusion direction.
- Thickness: cast is made to ISO 7823-1, which allows ±(0.4 mm + 10%), so 6 mm cast can measure 5.0 to 7.0 mm. Acrylite extruded holds about ±5% above 3 mm.
- Strength: about the same: both list roughly 10,000 psi tensile strength and 0.4 ft-lb/in notched Izod impact.
The differences side by side
| Cast acrylic | Extruded acrylic | |
|---|---|---|
| Laser engraving | Bright, frosty white mark with strong contrast | Clearer, glassier mark with less contrast |
| Laser-cut edge | Glossy, flame-polished look | Glossy, flame-polished look; melts a little more easily |
| Routing, drilling, sawing | Chips come off cleanly | Softer and gummier; can melt and re-weld behind the tool |
| Solvent bonding | Bonds well, a bit slower | Softens and bonds faster |
| Crazing from solvents and cleaners | More resistant | Crazes more easily, especially near cut or stressed edges |
| Thickness tolerance (6 mm sheet) | 5.0 to 7.0 mm (0.197 to 0.276 in.) | 5.7 to 6.3 mm (0.224 to 0.248 in.) |
| Max continuous service | 180 °F (82 °C) | 160 °F (71 °C) |
| Heating and bending | Higher forming temperature, little shrinkage | Forms at a lower temperature; can shrink up to 3% in one direction |
| Colors and specialty sheet | Widest range; thick sheet (3/4 in. and up) is mostly cast | Clear, common colors, and many framing and sign grades |
| Cost | Higher | Lower |
Figures are from Acrylite's cast and extruded data sheets; other brands are similar but not identical, so check the data sheet for the exact product.
Which engraves better, cast or extruded?
Cast, if you want the engraving to show. When a laser engraves cast acrylic, the surface vaporizes into a fine, frosted texture that reads as bright white, especially on clear sheet and in reverse engraving viewed through the front. Extruded acrylic tends to melt rather than frost, so the mark comes out clearer and harder to read. That's why awards, plaques, and edge-lit signs are almost always cast.
For cutting alone, both laser cut well and both get the glossy edge acrylic is known for. Acrylite notes that the laser edge on any acrylic carries high stress, and recommends annealing parts that will be glued or exposed to solvents. More on how engraving looks in acrylic.
Which glues better?
Thin solvent cements such as Weld-On 4 or SCIGRIP 4 work by softening the surface so the two pieces fuse. Extruded acrylic softens faster, so joints set quicker. The trade-off is that the same solvent can craze extruded sheet: fine cracks that spread from stressed areas such as laser-cut edges, drilled holes, and bends. Cast tolerates solvent better and gives fewer surprises, which is why we use cast for bonded boxes and display cases. How to glue acrylic and what crazing is and how to avoid it.
Thickness and fit
Because extruded sheet is squeezed between rollers, it holds its thickness well: Acrylite lists 1/4 in. (6 mm) extruded at 0.224 to 0.248 in. Cast sheet is allowed far more: the same nominal 6 mm cast can run 0.197 to 0.276 in. under ISO 7823-1, and big sheets are often thicker in the middle than at the edges. If you're designing tab-and-slot parts or press fits, that variation matters more than anything else on this page. See what each size actually measures.
Stress, heat, and bending
Extruded sheet carries orientation from being stretched as it's made. Heat it to forming temperature without a frame and it relaxes: Acrylite says its extruded sheet 0.118 in. and thicker shrinks up to 3% in the machine direction, while cast typically shrinks about 1.5%. For a single line bend this rarely matters. For a large part that has to come out at an exact size after forming, cast is more predictable. Cast also keeps its shape at higher temperatures, which helps near lights and in sunny windows. How to bend acrylic.
Which should you choose?
Choose cast acrylic for
- Anything engraved: signs, awards, plaques, trophies, edge-lit art
- Bonded boxes, display cases, and assemblies
- Parts that will be drilled, tapped, or machined heavily
- Parts near heat, such as light fixtures
- Thick parts; 3/4 in. and 1 in. sheet is almost always cast
Choose extruded acrylic for
- Plain cut-to-size panels: table covers, picture frame fronts, replacement windows
- Sneeze guards and dividers without engraving
- Slotted parts where even thickness matters more than engraving contrast
- Large quantities of simple shapes where the lower cost adds up
Not sure? Tell us what you're making on the make it in acrylic page, or compare both options in the instant quote, which lists clear cast and clear extruded side by side so you can see the difference in price for your exact part.
Questions
How can I tell if a sheet is cast or extruded?
Check the protective film first: manufacturers usually print the product name on it (Acrylite GP is cast, Acrylite FF and Optix are extruded). Without the film, engrave or cement a scrap: cast frosts white under a laser, and extruded softens and crazes faster with solvent.
Is cast acrylic stronger than extruded?
Their basic strength is nearly the same: both list about 10,000 psi tensile strength and 0.4 ft-lb/in notched Izod impact. Cast has better resistance to solvents and stress cracking and a higher heat rating, which makes it more durable around holes, edges, and glued joints.
Is cast or extruded better outdoors?
Both weather well, because UV resistance comes from the acrylic itself; Acrylite carries a 30-year light-transmission warranty on both its clear cast and clear extruded sheet. Choose based on the other factors: cast if it's engraved, bonded, or in hot sun, extruded for plain panels.
What is continuous cast acrylic?
It's cast between moving steel belts instead of individual glass molds, so it can be made in long runs. Plaskolite sells it as Optix-L. Ask for the data sheet of the exact product if engraving contrast or thickness matters, since continuous-cast lines vary.