In this work, heat capacities for three linear siloxanes (hexamethyl disiloxane (MM), octamethyltrisiloxane (MDM), and decamethyltetrasiloxane (MD2M)) in the temperature range of 205.15-395.15 K and for two cyclic siloxanes (octamethylcyclotetrasiloxane (D-4) and decamethylcyclopentasiloxane (D-5)) in the temperature range of 288.15-443.15 K have been measured with the help of a Tian-Calvert calorimeter. Furthermore, vapor pressures for the five mentioned compounds in the temperature range of 250-620 K and pressures from 2 mbar to 1 bar have been determined with the help of a Scott ebulliometer. The prediction of the heat capacities using the group contribution equation of state VTPR were improved by fitting the Twu parameters simultaneously to the new vapor pressure and heat capacity data. In addition, melting temperatures and heat of fusions for these five siloxanes have been measured using a differential scanning calorimeter (DSC). Furthermore, density measurements for the three linear siloxanes (MM, MDM, and MD2M) between 278 and 437 K and pressures up to 130 MPa were carried out using a vibrating tube densimeter. The densities were correlated with the TRIDEN model.