Flexural rigidity of a porous resin/Al laminate is estimated experimentally by means of the 3-point bending test. It can be seen from the results that the change in value of the flexural rigidity of the laminate is convex with respect to its thickness and thus there exists the optimal thickness. A new model that the neutral volume in which the bending stress does not occur exists around the neutral plane of the beam is devised for the explanation of the change in flexural rigidity with thickness.