This guide focuses on the fabrication choice — which acrylic machines, laser-cuts, bonds and thermoforms better, and why. For the full mechanical, optical, chemical and weathering property tables, see cast vs extruded acrylic: material selection data. We cast our own sheet — see China cast acrylic sheet manufacturer.
Cast acrylic has higher molecular weight than extruded acrylic, which makes it machine cleaner, polish brighter, resist solvents and crazing better, and thermoform more forgivingly — but its thickness tolerance is loose (±10–15%). Extruded acrylic holds tight thickness tolerance (±5%), costs 10–20% less, and laser-cuts and line-bends well, but is more prone to melting during machining and to stress cracking around bonded joints.
Both are 92%-transmission PMMA and look identical on a shelf. In fabrication they behave like different materials — and choosing the wrong one is a quiet source of cost overruns and field failures. Here’s the decision logic we apply when your drawing doesn’t specify.
The Comparison Table
| Property | Cast acrylic | Extruded acrylic |
|---|---|---|
| Molecular weight | High | Lower |
| Thickness tolerance | ±10–15% | ±5% |
| Sheet cost | Baseline | 10–20% lower |
| CNC machining | Clean chips, fine finish | Gummy, melt-prone at high speed |
| Laser cutting | Excellent, frosted-to-clear edge | Excellent, flame-polished edge |
| Line bending | Good | Excellent, wider process window |
| Thermoforming | Forgiving, even heating tolerance | Narrower window, sags faster |
| Solvent bonding | Strong, low craze risk | Craze-prone without annealing |
| Chemical/ESC resistance | Better | Worse |
| Available thickness | Up to 100 mm+ | Typically ≤ 25 mm |
| Optical polish quality | Best | Good |
Choose Cast When…
- The part is machined. Higher molecular weight means chips shear instead of smearing — better finish, tighter practical tolerances, half the melt-related scrap. All precision CNC work defaults to cast. → CNC machining
- Joints are solvent-bonded and loaded. Extruded acrylic’s internal stress plus solvent = crazing around joints, sometimes months later. Bonded enclosures, tanks and displays: cast, or extruded with a mandatory annealing cycle.
- The part is thick. Above 25 mm, cast is generally the only option anyway (blocks to 100 mm+).
- Edges are polished optical surfaces. Cast diamond-polishes to the best clarity.
- Chemical exposure exists (coolants, cleaners, lab reagents): cast’s ESC resistance buys service life.
Choose Extruded When…
- Thickness is a functional dimension. Sliding panels in tracks, parts mating with slots or extrusions: cast’s ±10–15% thickness variation will bite. Extruded ±5% usually drops straight in.
- The job is laser-cut flat parts at volume. Extruded costs less, laser-cuts with a beautiful flame-polished edge, and thickness consistency keeps focal height stable across nests — faster, cheaper, repeatable.
- The part is line-bent. Extruded heats and folds with a wider process window; it’s the default for bent covers, brochure-holder-type geometries and formed guards. → bending & thermoforming
- Cost rules and none of the cast triggers apply. 10–20% sheet saving is real money at volume.
The Traps
Trap 1 — extruded + solvent bond, no anneal. The classic delayed failure: joints craze weeks after delivery. If a design bonds extruded sheet, annealing before bonding is not optional. We quote it in automatically; a shop that doesn’t is deferring your failure, not saving you money.
Trap 2 — cast where thickness matters. A 10 mm cast sheet can legitimately arrive at 8.8–11.2 mm. If your groove is machined for 10.0 ± 0.3, that’s a lottery. Spec extruded, or spec the groove to be machined to the measured sheet.
Trap 3 — “acrylic is acrylic” purchasing. A buyer re-sources a proven cast-acrylic part to a cheaper quote that silently substitutes extruded; machining scrap and bond failures follow. Lock the grade on the drawing: “PMMA, cast, per ISO 7823-1″ (extruded: ISO 7823-2).
Trap 4 — assuming brand equals grade. Every major producer makes both cast and extruded lines. Brand name on a quote doesn’t tell you the grade; the datasheet does. We state grade + brand on every quote — material source: established international mills.
What If the Drawing Doesn’t Specify?
Our default logic as a fabricator: machined/bonded/thick/optical → cast; laser-cut flat parts, bent parts, thickness-critical fits → extruded. Every quote states which grade we assumed and why, so your engineer can override with one email instead of discovering it at inspection.
FAQ
Q: Is cast acrylic stronger than extruded? A: Mechanically they’re nearly identical in tensile/flexural terms. The real differences are processing behavior and stress-crack resistance, where cast wins, and dimensional consistency, where extruded wins.
Q: Which is better for laser cutting? A: Both cut well. Extruded gives the glossier flame-polished edge and lower cost; cast gives a lightly frosted edge that polishes brighter if the edge is a cosmetic surface.
Q: How do I call out the grade on a drawing? A: “PMMA, cast, ISO 7823-1” or “PMMA, extruded, ISO 7823-2”, plus color/grade code if applicable. One line prevents silent substitution.
Q: Do you stock both? A: Yes — cast and extruded in 3–100 mm across clear, frosted and colors; specialty grades (ESD, UV-filter, impact-modified) sourced per order in 5–15 days.
Not sure which grade your part needs? Send the drawing and application — the quote will specify grade, brand and the reasoning, within 12 hours.
Need the underlying numbers rather than the selection rules? The cast vs extruded PMMA property data reference sets out mechanical, optical, chemical and weathering data by grade.
Have a drawing or a question?
Send whatever you have — drawing, STEP file or sketch — and get a quote or DFM feedback within 12 hours.