A
metal foam is a cellular structure consisting of a solid
metal, frequently
aluminium, as well as a large volume fraction of gas-filled s. The pores can be sealed (closed-cell
foam), or they can form an interconnected network (open-cell foam). The defining characteristic of metal foams is a very high
porosity: typically 75–95% of the volume consists of void spaces making these
ultralight materials. The strength of foamed metal possesses a
power law relationship to its density; i.e., a 20
ense material is more than twice as strong as a 10
ense material.