CFM

In materials science, a metal foam is a material or structure consisting of a solid metal (frequently aluminium) with gas-filled pores comprising a large portion of the volume. The pores can be sealed (closed-cell foam) or interconnected (open-cell foam).[1] The defining characteristic of metal foams is a high porosity: typically only 5–25% of the volume is the base metal. The strength of the material is due to the square–cube law.
https://en.wikipedia.org/wiki/Metal_foam

Composite Metal Foam (CMF) https://l.smartnews.com/p-iYBN6xb/Y8cTjg 

Feather-light bulletproof metal foam to power up spacecraft, military gear