Thermal conductivities have been measured for three linear siloxanes [hexamethyl disiloxane (MM), octamethyltrisiloxane (MDM), decamethyltetrasiloxane (MD2M)], two cyclic siloxanes [octamethylcyclotetrasiloxane (D-4), decamethylcyclopentasiloxane (D-5)], and a mixture of SO mass % MDM + 50 mass % MD2M in the temperature range from 290 to 520 K and the pressure range from 500 to 10000 kPa using the transient hot wire method and correlated with a temperature pressure thermal conductivity relationship. Moreover, the thermal conductivities at atmospheric pressure were measured for MM, D-4, D-5, and MD2M. The data were compared with the available data from the literature for four compounds. Additionally, the viscosities of the five siloxanes were measured in the temperature range from 238 to 378 K at atmospheric pressure using a rotational Stabinger viscometer.