A type of chemical vapor‐sensing material made from multiwalled carbon nanotubes/hydroxyl propyl methyl cellulose/cellulose composite films were prepared in the room‐temperature ionic liquid 1‐butyl‐3‐methylimidazolium chloride ([BMIm]Cl). A typical negative vapor coefficient was observed when the film was placed in polar organic solvents, such as methanol and ethanol. The sensitivity of the film to vapors increased significantly with increasing temperature. Interestingly, the resistance of the films increased almost linearly with decreasing vacuum, and the changes in resistance with the vacuum show good repeatability. The surface morphology, thermostability, and stress–strain properties of the composite films were analyzed with scanning electron microscopy, thermogravimetric analysis, and an electrical universal testing machine, respectively. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41639.