Previous atomic force microscopy study showed that CNCs are resistant to water penetration, thus the swelling must be due to adsorption and clustering of water on the crystallite surfaces.[30] In addition, PEG is coated on the surface of CNC to provide steric stabilization. The PEG chains with hygroscopic nature spontaneously absorb water from moist air and enable easy access of water in and out of the chiral nematic film. To confirm the relationship between humidity and swelling of the cholesteric structure, the composite film was frozen in liquid nitrogen after equilibrated at different RH, and observed with FE-SEM after freeze-drying.