Water depth is the load.
Span is what breaks the panel.
Thick PMMA panel thickness — cast acrylic 100–600mm: span, safety factor, deflection, and casting constraints for viewing panel selection.
Every project that specifies panel thickness from water depth alone is starting from the wrong input. This note explains the five parameters that determine the correct thickness for a cast PMMA acrylic viewing panel — and why the methodology is the same whether the application is a residential pool wall or a full-scale oceanarium.
Summary for project owners: this explains why some thick acrylic panels yellow or crack within a few years — and how our casting and engineering standards prevent that to support a 30-year design life.
One-time cast vs. multi-layer — most clients don't know to ask
Most panels above 50mm in the market are multi-layer — sheets bonded together under heat and pressure. The bond line is usually invisible in normal conditions. Under certain lighting angles, or over time, it shows.
PG produces cast PMMA panels up to a maximum thickness of 600 mm, single-cast (one-time cast) up to 350 mm. Each single-cast panel is formed in one piece through its full thickness — no laminated layers, no bond line through the section, and no optical interface. For greater thickness or span, panels are joined by polymerization bonding into seamless builds — including a 49 m transparent pool wall in Vietnam, polymerization-bonded on site. Cast by bulk-monomer polymerization from 100% virgin Mitsubishi Chemical MMA.
Most clients don't know to ask which process was used. It's worth asking.
Five inputs. One of them is water depth. The other four are why water depth is not enough.
Thickness is the output of structural analysis — not the input to it. These five parameters go into the analysis. Water depth is one. For panels wider than about 1m, it is rarely the one that governs.
| Input | What it is | How it affects thickness | Common error |
|---|---|---|---|
| Hydrostatic pressure | Load from water depth at panel centroid (kPa) | Linear with depth — twice the depth, twice the pressure | Used alone to specify thickness |
| Visible span | Largest unsupported panel dimension between support edges | Bending stress increases with span² — doubling span requires ~4× bending resistance | Not stated, or confused with opening size |
| Boundary conditions | How edges are restrained — clamped or simply supported, 2 or 4 sides | Clamped 4-edge support can reduce required thickness 20–40% vs same panel on 2 sides | Assumed 4-edge simply supported when frame has only partial contact |
| Deflection limit | Maximum mid-panel movement under full hydrostatic load | Tighter limits drive thickness up independently of stress limits | Not specified — sealant fails when deflection exceeds joint capacity |
| Safety factor | Margin against characteristic PMMA tensile strength | Higher factor → thicker panel; factor 4.0 requires ~15% more thickness than 3.0 | Taken from an unrelated project, or not stated at all |
Why water depth alone does not determine acrylic panel thickness →
The relationship that most project specifications miss.
Water depth increases pressure linearly. Span increases bending demand with the square. For any panel wider than about 1m, the span-squared relationship overtakes the depth-linear relationship — and span becomes the governing parameter.
What span-squared means in practice
A panel with 1.0m span requires X thickness to meet its bending stress limit. A panel with 2.0m span needs thickness that provides approximately 4× the bending resistance. Because bending resistance is roughly proportional to thickness², the 2.0m span panel needs approximately 1.4× more thickness — not 2×. Non-linear, and larger than simple scaling suggests.
What this means when the opening changes
When a project increases opening size from 1.2m to 2.4m, thickness does not scale with the opening. The relationship is non-linear — and the correct thickness for the new span must be recalculated, not estimated by proportion from the previous project's thickness.
How thickness ranges across all five application types.
The same methodology applies to every application. What changes is the combination of span, depth, and safety factor — not the analytical framework itself.
| Application type | Typical thickness range | Governing parameter | Application note |
|---|---|---|---|
| Pool viewing wall — residential | 80–150mm | Span + boundary conditions | Pool Viewing Wall → |
| Pool viewing wall — hotel / feature | 120–220mm | Span + interface | Pool Viewing Wall → |
| Aquarium viewing panel — commercial | 100–400mm | Span + safety factor | Aquarium Panel → |
| Underwater tunnel panel | 150–400mm | Radius + arc span | Underwater Tunnel → |
| Oceanarium panel | 250–600mm | Span + depth + safety factor | Oceanarium Panel → |
Indicative only. All values require project-specific structural analysis and engineering sign-off. Do not use for procurement.
How we determine thickness — and who verifies it.
Panel thickness is determined by structural calculation and confirmed by finite element analysis (ANSYS). It is checked against the characteristic strength of cast PMMA (≈68–70 MPa), with the panel analysed integrally with its supporting structure (e.g. steel frame) — not in isolation. Water depth alone is not sufficient: unsupported span and boundary conditions govern. Our analyses are independently verified by Tongji Architectural Design Institute.
Structural FEA analysis examples — verified by Tongji Architectural Design Institute
Two worked examples from real ANSYS finite-element analyses. Example A is a delivered swimming-pool project; Example B is an engineering analysis study (feasibility) — not a built project. Both were analysed by Tongji Architectural Design Institute.
| Configuration | 7 acrylic panels; 5 fixed by a 4-side concrete frame (no middle beam); 2 fixed on concrete + steel structure |
| Water depth | 1.2 m (analysis run at 1.4 m head) |
| Material | Cast PMMA, tensile / compressive strength ≈70 MPa |
| FEA result @ 150 mm | Deformation ≈0.1 mm; steel max stress 22 MPa (far below yield) |
| FEA result @ 120 mm | Deformation ≈0.05 mm; steel max stress ≈10 MPa |
| Outcome | 120 mm recommended — satisfies panel strength and reduces load on the steel; consistent with field experience (1.2 m depth → 100 mm+) |
| Verification | ANSYS FEA by Tongji Architectural Design Institute |
| Configuration | Vertical pool panel, 4-side concrete frame, no middle beam |
| Panel size / depth | 6 m wide × 7 m high; water depth 7 m |
| Material | Cast PMMA, tensile strength ≈68 MPa, Young's modulus 3000 MPa |
| FEA result @ 400 mm | Deformation ≈0.01 mm; max stress 2 MPa (well below the characteristic strength of cast PMMA) |
| Outcome | 400 mm adequate |
| Verification | ANSYS FEA by Tongji Architectural Design Institute |
Engineering analysis study (feasibility), FEA-verified by Tongji — not a delivered project.
Worked examples are project-specific. They are not a water-depth-to-thickness lookup table — span, boundary conditions, and safety factor govern every result and require project-specific analysis.
Material — independently tested by SGS
Material independently tested by SGS: total luminous transmittance 93.1% (GB/T 2410), report No. SHIN1606027157MR-01 (2016). Report verifiable via SGS's official document verification service → evidence-packs.
Engineering Boundary Constraints: the TU Delft 3 m Cylinder Aquarium
The TU Delft 3-meter cylindrical research aquarium is fully cast PMMA — including the base. The cylinder wall and the base are joined by polymerization bonding, not a mechanical or dissimilar-material joint, giving a seamless, optically continuous structure. For a structural cylinder at this scale (3 m diameter x 3 m high x 100 mm wall), the wall thickness is governed by visible span, ambient temperature variance, and the required deflection limit (typically L/500 to L/750) — not water depth alone. Every PG Acrylic proposal is bound to project-specific Finite Element Analysis, independently verified by Tongji Architectural Design Institute, with material performance independently tested by SGS (93.1% light transmittance).
What thick cast PMMA panels actually require to produce.
Panels above 100mm are not cut from sheet stock. They are cell-cast in purpose-built moulds. The casting and annealing process imposes constraints that affect maximum dimensions, lead time, and residual stress — and these must be factored into design from the start, not discovered during procurement.
Casting cycle duration
- Panels above 150mm require extended casting cycles — days, not hours
- Above 300mm, cycle time extends significantly and temperature control becomes critical to avoid internal stress
- Casting cycle directly affects lead time from order to delivery
Annealing — not optional
- All thick cast PMMA panels must be annealed to relieve residual thermal stress from casting
- Annealing cycle duration increases with thickness
- Inadequate annealing produces residual stress that causes crazing in service — often not visible until the panel is under hydrostatic load
Maximum plan dimensions
- Maximum plan dimensions depend on casting facility and panel thickness
- Thicker panels are available in smaller maximum plan sizes — mould and oven dimensions are the limiting factors
- Very large panels may require bonded multi-piece construction regardless of thickness
Thickness accuracy in thick cast acrylic: how PG controls it
Cast PMMA naturally varies slightly in thickness across a large panel — this is inherent to the casting process. To guarantee the specified minimum, PG Acrylic produces to a positive tolerance: panels are cast from a mould set slightly above nominal (the positive tolerance varies with panel thickness). Panels running thick are polished down to the final dimension, and final thickness is confirmed by direct measurement — the most verifiable form of QC. Material performance is independently tested by SGS (93.1% light transmittance).
For structural viewing applications, the material specification is not optional.
Cast and extruded PMMA are both called acrylic. For panels above approximately 25mm in a structural viewing application, they are not interchangeable — and specifying the wrong one is not a substitution that can be corrected after fabrication. Structural viewing panels use cast (cell-cast) PMMA; extruded is a thin standard-sheet product not used for thick structural panels. Specify cell-cast PMMA, annealed, to the thickness and plan dimensions required by structural calculation.
Thickness selection — questions that come up on every project
How is the correct thickness selected for a structural PMMA acrylic panel?
Structural analysis considering hydrostatic pressure, visible span, boundary conditions, allowable deflection, and safety factor applied to characteristic PMMA tensile strength. Water depth alone is not sufficient. The analysis must be project-specific — scaling from a previous project is only valid if span, boundary conditions, and safety factor are identical.
Why does span govern thickness more than water depth in most projects?
Water depth increases pressure linearly. Bending stress in a flat panel increases with the square of span. For any panel wider than about 1m, span is almost always the governing parameter. A 2m-wide panel in 1.5m of water typically requires more thickness than a 0.8m-wide panel in 4m of water.
What safety factor is used for cast PMMA viewing panels?
Typically 3.0–5.0 applied to characteristic tensile strength, depending on application type, public or private occupancy, consequence of failure, and applicable design code. Residential pool walls typically use 3.0–3.5; public aquarium and oceanarium applications typically use 3.5–5.0. The project specification should state the factor explicitly.
What is the maximum thickness for cast PMMA acrylic panels?
Monolithic single-cast PMMA is produced up to about 350 mm. For greater thickness, panels are built by polymer-bonded construction up to 600 mm; panels above 200 mm require extended casting and annealing cycles. Maximum achievable thickness depends on the facility and must be confirmed for each project.
What is the difference between cast and extruded PMMA for structural viewing panels?
Structural viewing panels use cast (cell-cast) PMMA, not extruded. Cast PMMA has higher and more uniform molecular weight, which gives better resistance to crazing and solvent stress, superior optical clarity through thick sections, and the ability to be polymerisation-bonded into large, thick, near-seamless assemblies. Extruded PMMA has tighter thickness tolerance but lower molecular weight and is not used for thick structural viewing panels. PG supplies cast PMMA only.
Can the thickness from a previous project be reused?
Only if span, boundary conditions, and safety factor are identical. If any of these has changed — and even a small change in span has a significant effect on required thickness — the previous project's thickness cannot be scaled directly. A new calculation is required.
Is PG's thickness analysis independently verified?
Yes. Panel-and-structure models are analysed by finite element analysis (ANSYS) and independently verified by Tongji Architectural Design Institute. Worked examples — a delivered 1.2 m-depth pool resolved at 120 mm, and a 7 m-depth feasibility study at 400 mm — are shown above, with material properties independently tested by SGS.
How is the wall thickness of a large cylindrical acrylic aquarium determined?
It is governed by visible span, boundary/support conditions, ambient temperature variance and a deflection limit (typically L/500 to L/750) — not water depth alone. On the TU Delft 3 m research cylinder (3 m dia x 3 m high x 100 mm, fully cast PMMA with the base polymerization-bonded to the wall), thickness was set against project-specific FEA verified by Tongji Architectural Design Institute, with SGS-tested material (93.1% light transmittance).
How does PG Acrylic ensure thickness accuracy in thick cast acrylic panels?
Cast PMMA naturally varies slightly in thickness, so PG produces to a positive tolerance — casting from a mould set slightly above nominal, then polishing panels that run thick down to final dimension, with thickness confirmed by direct measurement. Material is SGS-tested at 93.1% light transmittance on the test specimen.
Does PG Acrylic's structural analysis account for seismic or other extreme load cases?
Yes, to the extent a project requires. PG Acrylic's finite element analysis is driven by the project geometry from the CAD and drawings, with hydrostatic water load as the primary case. Where the project or local code calls for it, additional load cases such as seismic and thermal effects are included in the analysis. Models are independently verified by Tongji Architectural Design Institute.
Does ASME PVHO-1 apply to aquarium, oceanarium or pool viewing panels?
ASME PVHO-1 is the safety standard for Pressure Vessels for Human Occupancy — vessels where people are inside under a pressure differential (submersibles, hyperbaric chambers, certain pressurised viewports). Most aquarium, oceanarium and pool viewing panels are not PVHO vessels: people stand on the dry side at atmospheric pressure with water on the other. PG Acrylic does not claim PVHO-1 certification; instead, panel thickness is determined by project-specific finite element analysis against the characteristic strength of cast PMMA with an appropriate safety factor, independently verified by Tongji Architectural Design Institute. Where a project genuinely involves human occupancy under pressure, PVHO-1 requirements should be confirmed with the project's structural engineer.
What thick cast PMMA looks like — and what it tells you about the specification.
The physical properties of correctly cast and machined thick PMMA are visible at the edge and corner. Optical clarity through section, machined face flatness, and corner geometry all reflect the casting and annealing process — and are the first thing a structural reviewer will ask about.
Material documentation — available for download.
The thickness calculation tells you the number. These documents tell you the material that number was calculated for. Both are required before procurement.
Related application notes
Thickness range and what we need from you.
Typical thickness range
200 – 500mm
One-time cast up to 350mm. Above 350mm, casting schedule and dimensional limits must be reviewed before order confirmation.
What to send us
Thick panel specifications require all five inputs: application type, water depth, unsupported span, boundary conditions, and safety factor. Water depth alone is not enough.
- Application type (pool, aquarium, tunnel, oceanarium)
- Water depth
- Unsupported span
- Boundary conditions (support on how many sides)
- Safety factor requirement if specified
Have a thick PMMA panel project?
Send us your dimensions, water depth, and installation type. We'll confirm whether the thickness works, what's missing, and what needs to be resolved before fabrication.