A series of thermosensitive films for firefighting applications were synthesized by two-step polymerization from two types of polyol and isophorone diisocyanate and by the formation of aqueous polyurethane dispersions. This study was conducted to clarify the influence of different parameters such as the type of polyol, the chain length of polyol, and the hard segment content on the chemical, thermal, mechanical and diffusion properties of the final films using ATR infrared spectroscopy, differential scanning calorimetry, thermogravimetric analyses, water vapor permeability, swelling behavior, contact angle measurement, and dynamic mechanical analyses. It was noticed that the humidity transfer was influenced by the soft segment crystallization. Indeed, it enhanced the chain mobility in bulk materials leading to an increase in water vapor permeability rather than in swelling. In contrast, low crystallization induced surface state modification resulting in higher swelling capacity.