The question of non-destructive testing of porous materials has always been of interest for the engineering profession. A number of empirically based MOE-MOR relations between stiffness (Modulus Of Elasticity) and strength (Modulus Of Rupture) of materials have been established in order to control quality without damaging or destroying the material or the building component considered. The efficiency of MOE-MOR relations for this purpose depends very much on the homogeneity of porous material considered. For building materials like wood and concrete of normal or lower quality with a number of irregularities only scattered MOE-MOR relations (clouds) can be established from which no really reliable results can be read.For homogeneously produced porous materials, however, like modern ceramics and high performance concretes MOE-MOR relations can be presented which are reliable. The present paper contributes to the theoretical research on non-destructive testing of such materials relating strength to stiffness and pore geometry.It is demonstrated that solutions for stiffness, tensile strength, and pore strength (damaging pore pressure, frost, fire) for some ideal porous materials can be determined theoretically only from knowing about pore geometry. Pore geometry is the very important common denominator which controls both stiffness and strength.The accurate results obtained are finally used to suggest generalizations with respect to strength in general (tensile, compression, flexural), pore strength, and stiffness versus more realistic pore systems. The expressions suggested are evaluated successfully against a number of experimental data reproduced from the literature.