The vapor pressures of low-volatility chemical warfare (CW) agents, their byproducts and degradants, and simulants are important physical data that are needed for accurate vapor generation, for filter modeling and testing, and for assessing the environmental fate of the materials. This report documents the measurement of the vapor pressure of 1,4-dithiane (DTH), a byproduct associated with vesicant chemical warfare agent bis-2-chloroethyl sulfide (HD), in the range of (296.65 to 376.95) K. By combining our measurements with a study of the thermodynamic properties of the compound in the subambient range, we were able to calculate Antoine parameters that can be used to extend estimates of the vapor pressure from T= (256.95 to 376.95) K. We have calculated a value of 10.6 Pa for the vapor pressure of the compound at 298.15 K. This contrasts with the accepted value of 107 Pa.