Pure polyurethane dispersions (PUDs) have been synthesised via the prepolymer mixing method, with two different systems i.e. solvent free and the solvent containing PUDs. Isophorone diisocyanate (IPDI), polypropylene glycol (PPG 2000) and dimethylolpropionic acid (DMPA) were the basic materials. The prepolymers were neutralised with triethylamine (TEA) prior to dispersion into the mixture of deionised water and chain extender, hydrazine monohydrate (HYD). The same procedures were repeated in the making of the solvent containing PUDs with 20 wt. % of N-methyl-2-pyrrolidone (NMP). The film properties were examined with Fourier transform infra-red (FT–IR) spectroscopy, stress-strain tests, dynamic mechanical thermal analysis (DMTA), modulated temperature differential scanning calorimetry (MTDSC) and transmission electron microscopy (TEM). The latex particle sizes were measured with a Malvern Zetasizer. It was found that the plasticizing effect of NMP caused reduction in the glass transition temperature, Tg, which also affected the performance of the sample, particularly the tensile strength and extensibility. Annealing the solvent based PUDs under certain conditions improved the properties due to the evaporation of the NMP that was trapped in the films. The solvent-free samples showed superior properties to the solvent-based ones.