Bulkheads and partitions
Foam-cored sandwich panels with aluminium face sheets form light, stiff, non-combustible partitions in accommodation and service spaces, replacing heavier steel-and-mineral-wool constructions.
Marine materials guide
Aluminium Foam for Maritime and Naval Applications
Closed-cell aluminium foam is a metal sponge: solid aluminium cell walls around sealed gas pores, at a fraction of the density of solid metal. On ships it is used as a light, non-combustible core for bulkhead and deck sandwich panels, as an acoustic and vibration damping lining in engine rooms, and as a crushable energy absorber. This guide explains its properties, where it fits on a vessel and how to specify it.
- Structure
- Closed-cell aluminium
- Density
- about 0.2 – 0.8 g/cm³
- Fire
- Non-combustible metal
- Forms
- Panels, sandwich cores, blocks
Why aluminium foam suits ships
Ship designers fight weight above the waterline, fire risk in accommodation and machinery spaces, and noise and vibration from engines and propellers. Aluminium foam addresses all three in one material, which is why naval architects and outfitting companies have adopted it for interior and protective structures.
Foam is produced by releasing gas inside molten aluminium (typically with a titanium hydride foaming agent and a calcium or ceramic stabiliser) or by heating a compacted mix of aluminium powder and foaming agent. The result is a rigid block of closed cells a few millimetres across, which is then sliced into panels or foamed directly between face sheets.
Because the cells are sealed, closed-cell foam does not soak up water, and panels at densities below 1 g/cm³ float. The aluminium matrix does not burn or release toxic smoke, it can be recycled with other aluminium scrap, and it absorbs large amounts of energy by crushing progressively at a nearly constant stress.
Typical properties of closed-cell aluminium foam
Foam properties depend mainly on density: doubling the density raises stiffness and crush strength far more than proportionally. The values below are typical ranges reported for closed-cell aluminium foams and should be confirmed with test data for the specific product and density ordered.
| Property | Typical range | Comment |
|---|---|---|
| Density | about 0.2 – 0.8 g/cm³ | Roughly 7 – 30 % of solid aluminium (2.70 g/cm³) |
| Porosity | about 70 – 93 % | Mostly closed cells, a few mm in diameter |
| Compressive plateau stress | about 1 – 15 MPa | Rises steeply with density |
| Elastic modulus | about 0.4 – 2 GPa | Far lower than solid aluminium (about 70 GPa) |
| Energy absorption | Several MJ/m³ up to about 30 MJ/m³ | Depends on density and how far the foam is crushed |
| Combustibility | Non-combustible | All-metal structure, no binder |
| Thermal conductivity | A small fraction of solid aluminium | Pores interrupt heat flow |
| Water absorption | Negligible for closed-cell foam | Cut edges expose some open cells |
Data are indicative ranges from published research on closed-cell aluminium foams. Each order is supplied with the measured density and test results agreed in the contract.
Where aluminium foam is used on a vessel
Deck and floor panels
Sandwich panels spread loads over light stiffeners. Foam cores add damping that reduces structure-borne noise transmitted into cabins.
Engine room acoustic linings
Perforated or surface-opened foam panels with an air gap behind absorb machinery noise, survive oil mist and heat, and do not shed fibres like mineral wool.
Enclosures and sound boxes
Acoustic hoods around generators, compressors and pumps use foam panels for absorption plus a solid skin for insulation.
Protective and crash structures
Foam crushes at nearly constant stress, so it is used in layered protective panels and fenders to absorb impact or blast energy before it reaches the main structure.
Buoyancy and void filling
Closed-cell foam adds reserve buoyancy in compartments and stiffens thin-walled sections without significant weight.
Fire safety and classification considerations
Materials used on classed ships must satisfy SOLAS fire-protection requirements and the rules of the classification society (for example DNV, ABS, Lloyd's Register or Bureau Veritas). Non-combustibility is demonstrated by testing to the IMO Fire Test Procedures (FTP) Code, which uses the ISO 1182 furnace test.
- Aluminium alloy structures have a lower melting point than steel, so fire divisions made with aluminium normally need insulation to meet A- or B-class integrity times
- Foam panels used as linings or partitions should be approved as part of a tested construction, not as a loose material
- Any adhesive used to bond face sheets to foam must also be assessed for fire, smoke and toxicity
- For structural use, panel strength and stiffness must be proven by testing to the class society's requirements
- Keep records of density, panel thickness and batch for each delivery so test reports can be linked to supplied material
Design, joining and corrosion protection
Sandwich panel design
Bending stiffness comes from the face sheets separated by the core. Choose foam density for shear strength and local crushing resistance under point loads.
Joining
Panels are bonded, mechanically fastened through inserts or framed in extruded aluminium profiles. Direct welding into the foam is not practical; weld to frames or face sheets instead.
Seawater exposure
Use marine-grade face sheets such as 5083 or 5052 and seal cut foam edges. Panels in wet spaces should be coated or anodised.
Galvanic contact
Isolate aluminium foam panels from steel hull structure and copper-alloy fittings with non-conductive spacers or sealants to prevent galvanic corrosion.
Acoustic treatment
Closed-cell foam reflects sound unless the surface is opened by drilling, perforating or rolling; an air cavity behind the panel moves absorption to lower frequencies.
Machining
Foam can be sawn, waterjet cut and milled. Cut faces show open cells, which should be filled or edged where moisture or dirt could collect.
Aluminium foam compared with other marine core materials
| Core material | Fire behaviour | Water uptake | Strengths | Watch-outs |
|---|---|---|---|---|
| Aluminium foam | Non-combustible | Very low (closed cells) | Damping, energy absorption, isotropic properties | Higher density than honeycomb for the same stiffness |
| Aluminium honeycomb | Non-combustible core | Can trap water if skins fail | Highest stiffness-to-weight in one direction | Little energy absorption sideways; needs sealed edges |
| PVC / PET foam | Combustible | Low | Light, easy to form | Fire restrictions in many ship spaces |
| Balsa wood | Combustible | Absorbs water if damaged | Low cost, good compression strength | Rot risk after water ingress |
| Mineral wool (linings) | Non-combustible | Absorbs water and oil | Good thermal and acoustic insulation | Fibres, needs protective facings, no structural strength |
Many vessels combine materials: honeycomb sandwich panels for floors where stiffness per kilogram is paramount, and foam panels where fire behaviour, damping and impact resistance matter more. See the honeycomb sandwich panel guide for the alternative.
How to specify aluminium foam for marine projects
- Define the functionStructural core, acoustic lining, energy absorber or buoyancy filler. The function sets density and treatment.
- Give dimensionsPanel length, width and thickness, plus tolerances and any edge or cut-out details.
- Set the density or performance targetA density range, or the stiffness, crush stress or sound absorption you need.
- Choose facings and finishBare foam, foam with bonded aluminium face sheets, perforated or coated surfaces.
- List approvals and testsClass society, FTP Code tests, density reports, mechanical or acoustic test data; mill certificates for face-sheet alloys.
- Agree deliveryPacking in crates to protect edges and faces; EXW, FOB, CIF or DAP terms to your yard.
References and standards
- IMO – International Code for Application of Fire Test Procedures (2010 FTP Code)
- SOLAS Chapter II-2 – Construction: fire protection, fire detection and fire extinction
- ISO 1182 – Reaction to fire tests for products: non-combustibility test
- Ashby, M.F. et al. – Metal Foams: A Design Guide (Butterworth-Heinemann)
- ISO 13314 – Mechanical testing of metals: compression test for porous and cellular metals
Aluminium (aluminum) foam for marine use: FAQ
Does aluminium foam float?
Closed-cell foam with a density below 1 g/cm³ floats, and most marine grades are well below that. Cut edges expose some open cells, so seal them where long immersion is possible.
Is aluminium foam fire-proof?
It is non-combustible and gives off no toxic smoke, but like all aluminium it softens and eventually melts at much lower temperatures than steel. Fire divisions still need a tested construction with insulation where class rules require it.
Can aluminium foam absorb engine noise?
Yes, once the closed surface is opened by perforating or rolling and the panel is mounted with an air gap. Untreated closed-cell foam mostly reflects sound, though it still damps vibration.
How is foam joined to the ship structure?
By adhesive bonding, mechanical fasteners through inserts, or by framing panels in aluminium extrusions that are welded or bolted to the structure. Isolate it from steel to prevent galvanic corrosion.
What density should I choose?
Lower densities suit acoustic linings and buoyancy; medium and higher densities suit sandwich cores and energy absorbers where crush strength matters. Give us the performance target and we will propose a density range.
Is aluminium foam approved by classification societies?
Approval applies to a specific product and construction, not to foam in general. Agree the class society, rules and tests at the start so test samples match the panels to be supplied.
Looking for lightweight, non-combustible panels for a vessel?
Tell us the application, panel sizes, density target and class requirements. We will propose foam material and test documentation.
