Aluminium foams have been recently proposed as filling reinforcements to improve impact behavior of hollow components used as protection systems in vehicles. In this study, aluminium foam filled stainless steel tubes have been prepared by directly foaming metal powder compacts inside the tubes. Attention was concentrated on the interface phenomena that characterize the core-shell interaction and the process parameters determining the metallurgical reactions between the two alloys. The formation of binary and ternary intermetallic compounds was observed at the aluminium/steel interface whenever the growth of the oxide layer on the foam surface in foaming was constrained. Compression tests of the reinforced tubes confirmed a maximized energy absorption in coincidence with the formation of the interface bonding. In those cases, extended foam intrusions into compressed tube folds were observed. The microstructural investigation revealed that in the transition zone the intermetallic layer strength was comparable to that of the foamed matrix.