A tension plate apparatus was designed for measuring volume of water outflow from samples of porous material as a function of time. Volume outflow was measured from samples of glass beads and sand at moisture tensions < 200 cm. of water. In the calculation of moisture diffusivity, published theory and procedures were used. The experimental volume outflow of water in the low moisture tension range of all porous materials studied did not agree with that predicted by presently developed theory. Agreement with theory apparently improved in the higher tension range. This disagreement of theory and experiment is not presently explainable. Values of moisture diffusivity were calculated by fitting the outflow data near (Q∞ ‐ Qt)/Q∞ equals 0.5. Although the accuracy of these moisture diffusivity values is uncertain, the general nature of the moisture diffusivity‐moisture tension relationship is shown.