Floating floor core
A foam or foam-sandwich layer between hull and crew floor crushes progressively, reducing peak acceleration at the occupants' feet and lower legs.
Defence materials guide
Military-Grade Aluminium Foam: Defence & Blast Applications
Closed-cell aluminium foam is used in defence equipment as a crushable layer that turns blast and impact energy into controlled deformation, while also adding stiffness, sound damping and electromagnetic screening at very low weight. This guide explains where foam fits in vehicles, shelters and munitions, which properties to specify, and how to design it in alongside armour plate.
- Material
- Closed-cell aluminium foam
- Density
- about 0.25 – 0.8 g/cm³
- Main role
- Blast and impact energy absorption
- Test method
- ISO 13314 compression
Why defence engineers use aluminium foam
Aluminium foam is solid aluminium with most of its volume replaced by sealed gas pores. At a density of roughly 0.25 – 0.8 g/cm³ it weighs a tenth to a third as much as solid plate, yet it still behaves like a metal: it does not burn, it conducts electricity, and it can be bonded, bolted or clad with sheet.
Its defence value comes from how it fails. Under compression, cell walls buckle and fold one layer at a time, so the stress stays almost flat while the foam shortens by 50 – 70 %. That long plateau lets a foam layer absorb a large amount of energy while capping the force passed to the structure or people behind it. A solid plate, by contrast, transmits a short, sharp load spike.
Foam does not stop bullets or fragments on its own. In protection systems it works behind or between hard layers: armour plate defeats the projectile or blast wave, and the foam spreads and slows what gets through. The US Army has tested aluminium foam panels for blast mitigation and for insensitive-munitions packaging, and defence laboratories in several countries have studied foam-cored sandwich panels for mine-protected vehicles.
Key properties and how they scale with density
Almost every property of a foam depends on its density. As a rough rule, plateau stress rises with density to the power of about 1.5 to 2, so a small increase in density gives a large increase in crush strength. Published laboratory data illustrate the spread: a closed-cell foam at about 0.3 g/cm³ crushes at around 1 MPa, while one near 0.8 g/cm³ reaches about 15 MPa.
| Property | Typical behaviour of closed-cell foam | Why it matters in defence |
|---|---|---|
| Density | 0.25 – 0.8 g/cm³ (solid aluminium 2.70) | Sets weight per square metre and almost every other property |
| Compressive plateau stress | About 1 MPa at 0.3 g/cm³ up to about 15 MPa at 0.8 g/cm³ | Defines the force at which the layer crushes; choose it below what occupants or equipment can tolerate |
| Densification strain | Typically 50 – 70 % | Usable crush stroke; thickness × densification strain = available travel |
| Energy absorbed per volume | About plateau stress × densification strain (e.g. 5 MPa × 0.6 ≈ 3 MJ/m³) | Lets you size the layer for a design energy |
| Fire behaviour | Non-combustible metal; no smoke or toxic gas | Safe inside crew compartments and magazines |
| Acoustic and vibration damping | Higher internal damping than solid plate | Reduces cabin noise and equipment vibration |
| Electromagnetic screening | Conductive cell walls reflect and absorb RF energy | Useful in shelters and electronics enclosures, depending on thickness and joints |
Values are indicative ranges from published research and differ between production routes. Specify a density band and require batch compression test results to ISO 13314 rather than relying on catalogue figures.
Blast-attenuating floors and armoured cabins
Under-body mines and IEDs load a vehicle in two ways: a local pressure pulse on the hull and a global upward acceleration of the whole vehicle. Floors are usually designed as layered systems. The outer hull (often 5083 or 5059 aluminium armour, or steel) deforms and vents the blast; an inner floor sits on a crushable layer that limits how much of the hull deflection and acceleration reaches the crew.
Sandwich armour panels
Foam cores between two aluminium skins raise bending stiffness and absorb energy. Research on foam-cored sandwich plates has reported 50 – 150 % more energy absorption than solid panels of comparable mass.
Spall and trauma backing
Behind a hard face, a foam layer spreads load from a stopped projectile and limits back-face deformation transmitted into the structure.
Cabin and container walls
Foam-cored wall panels in armoured cabins and protected containers add stiffness, damp noise and give a non-combustible lining.
Shelter doors, missile structures and shielded rooms
- Shelter and bunker doors: foam-cored door leaves stay light enough to open by hand while gaining stiffness, overpressure resistance and acoustic insulation. See our overview of military shelter systems and shelter profiles.
- Missile and munition structures: foam is used as a crushable buffer in containers and launch structures, and in insensitive-munitions packaging to slow the reaction of neighbouring rounds.
- Electronics shelters: conductive foam panels, combined with continuous electrical bonding at joints, contribute to radio-frequency screening of communications and command shelters.
- Equipment mounts: foam blocks under sensitive equipment absorb shock from transport drops and weapon recoil.
- Naval topside panels: light, non-combustible foam sandwich panels for superstructure partitions where fire and weight matter together.
How to size and specify a foam layer
- Set the force limitDecide the maximum load or acceleration the protected item can tolerate. Divide by the loaded area to get the target plateau stress.
- Choose densityPick the density band whose plateau stress sits just below that limit. Too dense and the foam acts like a solid block; too light and it bottoms out.
- Check the energyMultiply plateau stress by densification strain and by volume. If the design energy is larger, increase thickness rather than density.
- Design the facesBond or mechanically fix aluminium skins (5083, 6061 or armour grades) so that load spreads evenly into the core.
- Verify by testRun quasi-static compression to ISO 13314 on every batch and, for qualification, dynamic or live-fire tests on full panels.
Supply forms from Metline
Metline supplies closed-cell aluminium foam as cut panels and blocks, and as sandwich panels with aluminium skins, together with the aluminium armour plate, sheet and extrusions that frame them. Panels can be cut to drawing. Each lot can be supplied with density and dimensional checks and compression test results, and we ship worldwide from Mumbai.
Typical specification items
- Foam type
- Closed-cell; open-cell available for acoustic duties
- Density band
- For example 0.40 ± 0.05 g/cm³; agreed per application
- Format
- Panels, blocks, cut shapes, foam-cored sandwich panels
- Skins
- 5083, 5052, 6061 sheet or armour plate, bonded or fixed
- Documents
- Inspection report, ISO 13314 compression data, material certificates for skins
References and standards
- ISO 13314 – Compression test for porous and cellular metals
- US Army – Army tests aluminum foam for protection against blasts (2020)
- DRDO – Brief write-up on aluminium foam technology
- Ashby, Evans, Fleck, Gibson, Hutchinson, Wadley – Metal Foams: A Design Guide (Butterworth-Heinemann)
Military aluminium foam: frequently asked questions
Can aluminium foam stop bullets?
Not on its own. Foam is a crushable energy absorber. In armour systems it sits behind or between hard layers such as aluminium or ceramic armour, where it spreads load and reduces back-face deformation.
What density of aluminium foam is used for blast protection?
It depends on the force limit of the protected structure. Densities of about 0.3 – 0.6 g/cm³ are common for crush layers, with denser foam used where higher plateau stress is required. The correct value comes from the load calculation, not a standard figure.
How is aluminium foam tested?
Quasi-static compression to ISO 13314 gives plateau stress, densification strain and energy absorption. Defence programmes add dynamic, drop or live-fire tests on full panels.
Does aluminium foam provide EMI shielding?
Its conductive cell walls attenuate radio-frequency energy, and foam panels are used in shielded shelters. Actual shielding effectiveness depends on thickness, density and, above all, on continuous electrical bonding at panel joints, so it should be measured on the assembled enclosure.
Is aluminium foam fireproof?
It is non-combustible and gives off no smoke, but aluminium melts at about 660 °C, so foam is not a high-temperature fire barrier. It is valued in crew spaces because it does not feed a fire.
Can you supply foam sandwich panels with armour-grade skins?
Yes. We can supply foam cores with aluminium skins in 5083, 5052, 6061 or armour grades, cut to drawing and shipped worldwide with test documentation.
Need aluminium foam for a defence project?
Tell us the application, panel size, density band and quantity. We will reply with options, test data and a delivered price.
