The purpose of this in vitro study was to evaluate the characterization and physical properties of hard chairside reline material modified with cellulose nanocrystals (CNC). One hard chairside reline material were tested: Soft-Comfort (SC), into which 0.25%, 0.5%, 0.75% or, 1.0% of CNC was incorporated; the control group had no CNC. Specimens were prepared and The Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM), Vickers hardness (VH), surface roughness (SR), surface free energy (SFE) and were performed. The addition of CNCs at 0.5%, 0.75% and 1% into SC increased VH (One-Way ANOVA/Welch, Games-Howell post-hoc test, p=.000); 0.75% decrease SFE (One-Way ANOVA, Bonferroni post-hoc test, p= .028); 0.75% and 1% showed similar to control (One-Way ANOVA/Welch, Games-Howell post-hoc test, p =.019) on the SR.