can therefore only be deformed once. They are light (typically 10–25% of the density of an identical non-porous alloy; commonly those of aluminium) and stiff and are frequently proposed as a lightweight structural material. However, they have not been widely used for this purpose. Closed-cell foams retain the fire resistance and recycling potential of other metal foams, but add the property of flotation in water. Stochastic foam A foam is said to be stochastic when the porosity distribution is random. Most foams are stochastic because of the method of manufacture: Foaming of liquid or solid (powder) metal Vapor deposition (CVD on a random matrix ) Direct or indirect random casting of a mold containing beads or matrix Regular foam A foam is said to be regular when the structure is ordered. Direct molding is one technology that produces regular foams with open pores. Metal foams can also be produced by additive processes such as selective laser melting (SLM). Plates can be used as casting cores. The shape is customized for each application. This manufacturing method allows for "perfect" foam, so-called because it satisfies Plateau's laws and has conducting pores of the shape of a truncated octahedron Kelvin cell (body-centered cubic structure). Hybrid foam Hybrid metal foams typically have a thin film on the underlying porous substrate. Coating metal foams with a different material has been shown to improve the mechanical properties of the metal foam, especially because they are prone to bending deformation mechanisms due to their cellular structure. The addition of a thin film can also improve other properties such as corrosion resistance and enable surface functionalization for catalytic flow processes. To fabricate hybrid metal foams, thin films are deposited onto a foam substrate with electrodeposition at room temperature. A two-electrode cell setup in a Watt's bath can be used. Recent studies have demonstrated issues with the uniformity of the thin-film due to the complex geometry of metal foams. Issues with uniformity have been addressed in more recent studies through the implementation of nanoparticle thin films, leading to improved mechanical and corrosion resistance properties. Recent studies on hybrid foams have also been used to address non-renewable energy resources. Transition metal hybrid foams have previously been fabricated through a combination of electrodeposition and hydrogen bubbling processes to enhance the diffusivity of fluids through the porous material and improve the electrical properties for enhanced charge transfer. Thus, such foams can be