Taylor tests have been commonly employed to determine dynamic yield stress of solids at a high strain rate. In this paper, the original Taylor model is extended in order to provide a theoretical basis for testing ductile porous materials. The key difference between solids and porous materials in this respect is that porous materials are compressible and their density changes with the compressive strain. Calculations have been made for porous materials with a relative density that is a linear function of compressive strain. The final length of the projectile after impact, L1/L, is plotted against parameter ?0U2/Y (see Fig. 9) and this plot is used in a Taylor test to determine the dynamic yield stress. The mean strain rate of the test can be estimated from Eqs. (21) or (22). In a companion paper (Int J Impact Eng), experiments for dynamic yield stress of porous materials will be reported based on the present theoretical analysis.