Different cell sizes of foamed or cellular glass were tested in tension (the Brazil test), flexure and compression at various stress rates. It was observed that the strengths increased with stress rate and also varied with the macrostress state. In all the tests the smaller cell sizes were stronger, the strengths varying as the inverse square root of the cell size. Analysis of the tensile (the Brazil test) results suggests a cumulative damage failure model where the critical flaws developed by the sequential failure of adjacent cell walls by a slow crack growth process. The K Ic value of this particular cellular glass is estimated to be about 0.087 MPa m 1 2 . Consideration of the flexural and compressive strength measurements suggests a shear mode of failure and that the K IIc and the K IIIc of these cellular glasses may substantially exceed their K Ic value.