ESDU 02003 presents values of thermal conductivity@ dynamic viscosity@ specific heat capacity and Prandtl number of the vapours of 26 halogenated methanes in the dilute or ideal gas. The data for thermal conductivity and viscosity result from the correlation of experimental data extracted from the literature. For specific heat capacity@ the data were calculated from best fits to values published by the Thermodynamics Research Center. The data correlation procedures used to obtain the values of thermal conductivity@ viscosity and specific heat capacity are described and the effects of pressure are indicated. The experimental data used are believed to be the most reliable available and have been reviewed and suitably extended. The data are presented in tabular form at intervals of either 20 K or 20 degree Celsius and as equations (except for the Prandtl number). The temperature range covered is from below the normal boiling point to at least 600 K. The likely uncertainties in the values are noted in the text@ and the sources of the data for each compound are listed.