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 thick structural panels are always cast.
For structural and large-format viewing panels — aquariums, oceanariums, pools and tunnels — cast (cell-cast) PMMA is used, not extruded. Cast PMMA has higher, more uniform molecular weight, which gives better resistance to crazing and solvent stress, superior optical clarity through thick sections, and the ability to be polymerization-bonded into large, thick, near-seamless assemblies. Extruded PMMA has tighter thickness tolerance and lower cost in thin standard sheet, but lower molecular weight and is not used for thick structural viewing panels. 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 | Higher, uniform | Lower |
| Crazing / solvent resistance | Better | More susceptible |
| Clarity in thick sections | Superior | Degrades |
| Large / thick / seamless panels | Yes — bondable to 600 mm | No |
| Thermoforming (curves, cylinders, tunnels) | Yes | Limited |
| 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?
Cast (cell-cast) PMMA, not extruded. Cast has higher, more uniform molecular weight, better crazing/solvent resistance, superior clarity in thick sections, and can be polymerization-bonded into large seamless panels up to 600 mm. Extruded is for thin standard sheet and is not used for thick structural panels.
Why is cast acrylic better than extruded for thick or large panels?
Higher molecular weight gives better resistance to crazing and solvent stress and better optical clarity through thick sections; cast panels can also be polymerization-bonded into large, near-seamless assemblies. Extruded has lower molecular weight and is limited to thin standard sheet.
Can extruded acrylic be used for a large aquarium or tunnel?
Not for the structural viewing panels. Large aquariums, tunnels and pools use thick cast PMMA; extruded acrylic is a thin standard sheet product not suited to thick, load-bearing or curved viewing panels.
Go deeper
For how cast PMMA thickness is determined, see Thick PMMA Panel Thickness. For cast acrylic versus glass, see Acrylic vs Glass.