The thermal conductivity of a new fluoroalkane, R365mfc (1,1,1,3,3-pentafluorobutane), important for the production of polyurethane rigid foams, was measured using a transient hot wire method, at temperatures between 336.85 K and 377.4 K. The extended corresponding states theory was used successfully to predict the results, with an average absolute deviation of 0.5%. The vapor pressure (302.90 K to 358.15 K) and the liquid density (289.15 K to 413.15 K, at pressures up to 9.85 MPa), were measured, using the dynamic method and the vibrating tube method, respectively. The critical point of R365mfc, required for the thermal conductivity calculations, was calculated with the correlations of Dohrn (J. Supercrit. Fluids 1992, 5, 81) using the normal boiling point and the liquid density at 20 degreesC as input data.