This data article contains the dynamic mechanical thermal analysis (DMTA) results for sheets made from cellulose fibers partially converted to dialcohol cellulose. See Larsson and Wågberg [1] for a description and characterization of the material as well as how the material is produced. See also Linvill et al. [2] for tensile testing and 3-D forming of the material. The DMTA tests were conducted at four different relative humidity levels: 0, 50, 60, and 70 % RH, and the temperature was swept between 10 and 113 °C. The DMTA results enable the understanding of the elastic, viscoelastic, and viscoplastic mechanical properties of this material at a wide range of temperature and relative humidity combinations.