This study verifies a novel approach to determine the thermal conductivity developed by the first two authors (Tomanek and Stutts) [1] as applied to additively manufactured selective laser melted stainless steel 304L specimens having a range of 1.4 to seven percent porosity. The selective laser melting technique is highly dependent on the process parameters used, unlike traditionally manufactured materials, and can cause the thermal, electrical, and mechanical properties to vary considerably from the bulk alloy. For this study, the thermal conductivity and several auxiliary parameters were estimated using a Levenberg-Marquardt nonlinear least squares algorithm. The parameter estimation used a model of a one-dimensional transient heat diffusion PDE with a closed-form solution of a slender rod under forced convection. In addition to the thermal conductivity's dependency on porosity, the correlated porosity dependency on electrical conductivity was examined. The results were corroborated by mechanical tensile tests as well. The stainless steel 304L selective laser melted specimens saw a degradation of mechanical, thermal, and electrical performance with increasing porosity.