Material guide Cast vs extruded
Cast and extruded acrylic are both PMMA. They are not the same sheet. Cast is the usual choice for a polished edge, a solvent joint, and a face the customer looks at. Extruded is the usual cost choice for a thin back, a divider, or a part whose edge will not be polished. The nickname “acrylic” does not say which one you will get.
The short answer
Decision rule. If the edge faces the customer, or the joint is solvent-bonded and meant to disappear, start with cell-cast acrylic. If the part is thin, hidden, or a cost panel whose edge can stay frosted, extruded acrylic is often enough. On a box, the two routes can sit in the same product — cast on the show faces, extruded on a hidden back — if you say so.
How the two sheets are made
Cell-cast acrylic is poured as monomer between plates and cured. That is the sheet ISO 7823-1 covers. Display shops use it because it machines, polishes, and solvent-bonds in a predictable way. It is the usual sheet above the thin gauges, and the usual sheet when the edge is part of the look.
Extruded acrylic is melted and pushed through a die. That is the sheet ISO 7823-2 covers. It is generally the lower-cost route and often the more consistent thickness. Laser-cut edges are typically frosted and need a separate polish if they face the customer. Heat bending and solvent joints are more sensitive than on cast.
Both are PMMA. A trade name — Plexiglass, Perspex, Lucite — does not tell you which process made the sheet in your quote.
What changes for the buyer
Directional. Grade and mill move the details. This is not a datasheet.
| Cell-cast | Extruded | |
|---|---|---|
| Usual role | Show face, polished edge, bonded case | Back, divider, thin non-show panel |
| Edge after laser or saw | Polishes cleanly; the usual cube edge | Often frosted; polish is extra and less even |
| Solvent joint | The normal clear joint on a display box | Possible, more sensitive; not the default for a disappearing joint |
| Thickness | Often wider variation across a sheet | Often tighter; helpful for slots and fits |
| Heat bend | Works; practice differs from extruded | Common for simple bends; can whiten or bubble if the heat is wrong |
| Relative sheet cost | Higher | Lower |
Do not copy a “30 percent cheaper” or a yellowing-year claim from a brochure into a specification. Cost depends on thickness, mill, and the stations after the sheet. Yellowing depends on grade and exposure, not on the word cast alone.
Which route for which part
Polished display cube
Cast on every face the customer sees, and on every solvent joint. A hidden base can be extruded if you accept the difference and write it down.
Simple bent brochure holder
Extruded is often enough: one bend, no polished show edge, cost matters. Say extruded so the quote is not priced as cast.
Slotted assembly
Extruded’s more consistent thickness can help the fit. If a slotted edge is also a camera edge, you are back to cast plus a polish.
Thick optical block or plinth
Cast. Extruded sheet is not the usual route once the part is thick and the edge is finished.
Those constructions, in acrylic, are the usual retail set: boxes, trays, and display stands.
Thickness, without a fake number
Cast sheet is cured between plates. Thickness can vary more across a sheet than extruded sheet of the same nominal gauge. Extruded sheet is generally more uniform, which is why it is preferred for press fits and interlocking slots.
The allowed variation is in ISO 7823-1 for cast and ISO 7823-2 for extruded, and then in the mill’s own tolerance for that grade. Quote the standard or the mill sheet. Do not invent a plus-or-minus percent on a buying guide and treat it as universal.
Design joints with a fit allowance either way. A nominal 5 mm wall is a name. The mating part has to survive the real sheet.
What to write on the RFQ
- PMMA, then cast or extruded — per member if they differ.
- Which edges are polished, and to what level.
- Which joints are solvent-bonded.
- Nominal thickness, and whether a fit depends on it.
- Whether a named mill grade is required, or any cell-cast / any extruded is acceptable.
A quote that does not state the route is not comparable to one that does. Ask before you award on price.
Sanait fabricates acrylic displays and will read a brief as needing a stated route. How a brief is taken is on the FAQ. Scope is on the about page.
FAQ
Is cast acrylic better than extruded?
Better for a polished edge and a clear solvent joint. Not automatically better for a thin hidden panel, where extruded is often the correct and cheaper sheet.
Can I solvent-bond extruded acrylic?
Yes, with more care, and the joint is less forgiving than cast-to-cast. For a disappearing joint on a show box, specify cast.
Why is cast more expensive?
The sheet itself usually costs more, and the parts that need cast usually also need polish and joints. You are often paying for the route and the stations, not for a brand word.
Does cast yellow less?
Route is not a weathering guarantee. Grade and exposure decide. Ask for the grade if the face sits in a window. Do not treat “cast” as a UV specification.
Can one box use both?
Yes, if you assign them: cast on show faces and joints, extruded on a hidden back or divider. Write it. A silent mix is how two “acrylic boxes” become different products.
What if the quote only says acrylic?
Ask cast or extruded before you compare price. The missing word is the specification.
Sources
Tolerances and characteristics belong to the standards and the mill. This page does not restate them as universal percentages.
- ISO 7823-1:2003, Plastics — Poly(methyl methacrylate) sheets — Part 1: Cast sheets. iso.org
- ISO 7823-2:2003, Plastics — Poly(methyl methacrylate) sheets — Part 2: Extruded sheets. iso.org
- “Poly(methyl methacrylate).” Wikipedia. en.wikipedia.org
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