The paper summarizes published data and also deals with classification, structure and properties of Mg based gasars – a new porous materials based on original findings obtained by author. Gasar pore size may be varied between 5 microns and 10 mm as desired, and the amount of porosity may reach 75%. The pore wall surface is always entirely clean. Possible applications of the new class porous materials in modern aircraft and space industry are addressed. Special place in the paper was dedicated to the porous metals that were manufactured by the method of gas eutectic transformation. Making the material consists of two steps: 1. Mg o Mg-alloy melt charging with hydrogen to reach the eutectic composition, and 2. The melt solidification in a conventional or continuous casting mold. The main process variables that govern the amount of porosity and the size, shape, and orientation of the pores are the hydrogen level in the melt, gas pressure over the melt in solidification, direction and rate of heat removal, and alloy chemical composition. Changing these variables, one can control the pore structure over a wide range (Patent USA #5181549). Mg-gasars formed by gas-eutectic reaction are particularly promising. Among the advantages of gasars over conventional porous metals, are: - improved strength and rigidity, - flexibility in regard to the permeability, - feasibility of control over pore shape and orientation, - ease of fabrication and relatively low cost, - good weldability and fabricability. Mg-gasars are suited for machining and forming, allow hardening by conventional heat treatment, possess unique damping capacity, can be produced with a heat conductivity value lower or greater than the one for the monolithic material and have good capacity to absorb vibrations and sounds. In future these features may make gasars common structural and a base for a number of composites.