The plasticity of a number of solders at wiping temperatures has been determined by compression tests between parallel plates. The character of the flow is found to be that corresponding to a linear relation between shearing stress and a fractional power of the velocity gradient. This corresponds approximately to a relation between rate of compression(dhdt)and sample height (h) given by the equation:dhdt = khb, in whichkandbare constants, of whichbis independent of the test conditions. For viscous materialsb= 5.0; for most soldersbis greater than 5.0, and increasing values ofbare associated with lower temperature gradients of plasticity. It is shown that a solder must have a low temperature gradient of plasticity in order to be properly wiped, and that determination of the value ofbby means of a plasticity test can therefore be used to evaluate the working properties of a solder.A number of factors upon which the plasticity of wiping solders and the porosity of wiped joints may depend have been investigated. In particular, it is shown that segregation is not responsible for porosity, but that the latter may be dependent upon the particle size of the solid phase at wiping temperatures. The relation of particle size to the wetting power of the liquid phase is discussed.