Cellulose is one of the most abundant biopolymers on earth, occurring in wood,cotton,hemp and other plant based materials and serving as dominant reinforcing phase in structures. Cellulose contains both amorphous and crystalline structures. Crystalline nano cellulose (CNC), also called nanocrystalline cellulose (NCC), is typically a rigid rod–shaped monocrystalline cellulose domain (whisker) with 1-100 nm in diameter and tends to hundreds of nanometers in length. Moreover, it also provides high aspect ratio, large surface area, unique tensile strength (0.8-10 GPa), low density and high Young’s modulus (100-170 GPa). Therefore NCC can be widely used for polymer composite reinforcement, enhancement of thermal stability and mechanical properties. In this study, crystalline nanocellulose was obtained from different sources such as cotton linter, jute and kenaf bio-sources via pulping, bleaching, acid hydrolysis, neutralization and lyophilization to increase crystallinity of CNC. More than 60% crystallinity was obtained from kenaf and jute bio-sourced NCC from DSC (differential scanning calometry) analysis. NCC was mixed with polyol mixture at different loading in order to see bio-source effect on properties of rigid Polyurethane Foam. High shear mixer (20000 rpm) and probe ultrasonication where needed was used to improve final dispersion within the mixture. Polymeric isocyanate (MDI) and polyol were reactive injection molded to prepare foam samples. The resulting polyurethane was characterized by SEM (Scanning electron microscope), thermal conductivity measurement, compressive strength and pycnometry. Results showed that either jute, kenaf or cotton based NCC content improved the thermal conducvity of rigid PU foams due to the nucleation effect during reactive injection molding with min. 1mW/mK decrease from the reference value of 20.25 mW/mK. Best mechanical property improvement was obtained from cotton based NCC with min. 20% increase in compressive strength. This improvement was obtained at much lower kenaf based NCC loadings which was attributed to the relatively higher percent crystallinity with less hemicellulose content within the PU matrix.