Polyurethane (PU) resin systems exhibit superior strength and damage tolerance relative to unsaturated polyester and vinylester pultrusion resins. Also, high pultrusion line speeds can be achieved using PU resins. A previous study, has successfully evaluated pultrudable PU with aromatic isocyanate and soy-based polyol (with 20% soy content). The performance of the soy-based resin is comparable to the base PU resin. However, aromatic PU based composites have poor environmental stability under UV light exposure and require specialized painting to provide protection. Aliphatic PU resins provide improved UV resistance but exhibit lower mechanical performance in comparison to aromatic polyurethanes. In the proposed work, we will investigate pultrudable PU resin systems with aromatic and aliphatic isocyanates, and soy-polyol. Neat resin coupons and pultruded composite parts will be manufactured using the developed aromatic and aliphatic PU resin systems. Also, parts will be manufactured by incorporating nano-engineered fillers in the aliphatic soy-based PU resin system to compensate the loss of mechanical performance over aromatic PU resins. The cure kinetics of polyurethanes will be studied by differential scanning calorimetry (DSC) and the reaction rates of the aliphatic and aromatic polyurethanes will be compared. Mechanical performance will be evaluated by conducting tensile, flexure and impact tests. The economics of aromatic system and aliphatic systems will be assessed.