Cellulose nanocrystals (CNC) have been used as reinforcement in polymer nanocomposites to improve their mechanical and thermal properties. In this study, we synthesized CNC-reinforced polyurethane foams (CNC-PUF), which are the most important component of liquefied natural gas and liquefied petroleum gas insulation systems, using various CNC loadings. The temperature-dependent mechanical and thermal characteristics of the CNC-PUF samples were investigated. In addition, the microstructural and X-ray diffraction investigations of the composite samples were performed. It was observed that the thermal and mechanical characteristics of the CNC-PUF sample with 0.6 wt% cellulose nanocrystals were superior to those of neat PUF under room and cryogenic temperatures. These properties showed a significant dependence on CNC loading, temperature, and foam density.