Cast or extruded acrylic?
For structural viewing panels, it's cast.
Cast (cell-cast) PMMA versus extruded acrylic for aquarium, oceanarium, pool and tunnel viewing panels — and why PG uses cast PMMA for thick structural viewing panels.
PG Acrylic uses cast (cell-cast) PMMA for structural and large-format viewing panels. Cast and extruded PMMA are both acrylic materials and both can be thermoformed and bonded, but their molecular weight, forming behavior, available thickness ranges and fabrication routes differ. Cast PMMA typically has higher molecular weight and is available in much thicker sheet or block forms; PG therefore uses cast PMMA for thick structural viewing panels and polymerization-bonded assemblies. Extruded PMMA is commonly supplied as standard sheet with tighter thickness tolerance. PG Acrylic supplies cast PMMA (20–600 mm).
Summary for project owners: "acrylic" comes in two types — cast and extruded. Large aquariums, pools and tunnels are built from cast acrylic because it stays clear, resists cracking, and can be bonded into big seamless panels. Extruded is a thin, low-cost sheet material and is not used for these structures.
Cast vs extruded PMMA — the differences that matter for viewing panels
| Property | Cast (cell-cast) PMMA | Extruded PMMA |
|---|---|---|
| Molecular weight | Typically higher | Typically lower |
| Crazing / solvent behavior | Depends on grade and fabrication; cast is PG's selected route for structural work | Depends on grade and fabrication |
| Thick-section availability | Available in thick sheet / block forms | Commonly supplied in thinner standard sheet |
| PG structural viewing-panel process | Used for thick panels and polymerization-bonded assemblies | Not used by PG for thick structural viewing panels |
| Thermoforming | Yes — forming window differs by grade/process | Yes — forming window differs by grade/process |
| Thickness tolerance | Slightly looser, polished to spec | Tighter |
| Typical use | Structural large / thick / curved viewing panels | Thin standard sheet |
Cast vs extruded — common questions
Cast or extruded acrylic — which is used for aquarium and structural viewing panels?
PG Acrylic uses cast (cell-cast) PMMA for thick structural viewing panels. Cast PMMA typically has higher molecular weight and is available in much thicker sheet or block forms. Extruded PMMA is a valid acrylic material and can also be thermoformed and bonded, but PG does not specify it for thick structural viewing panels.
Why is cast acrylic better than extruded for thick or large panels?
PG selects cast PMMA because its molecular-weight profile, thick sheet/block availability and fabrication route suit PG's structural viewing-panel process. Extruded PMMA has a different forming window and is commonly supplied as thinner standard sheet; suitability should be checked against the actual product grade and project requirements.
Can extruded acrylic be used for a large aquarium or tunnel?
Extruded PMMA is a valid acrylic material and can be thermoformed and bonded. PG Acrylic, however, does not specify extruded PMMA for thick structural viewing panels; those projects use cast PMMA within PG's manufacturing and bonding process. Final material selection should follow the project design and the relevant manufacturer data.
Go deeper
For how cast PMMA thickness is determined, see Thick PMMA Panel Thickness. For cast acrylic versus glass, see Acrylic vs Glass. If the material question comes from a specific project, the application pages carry the supplier scope and project proof: aquarium acrylic viewing panels and underwater tunnel acrylic panels.