A two-step sequential biomass liquefaction process was developed to produce bio-based polyols and polyurethane (PU) foams using crude glycerol as a liquefaction solvent. The first step, acid-catalyzed liquefaction, was highly effective in liquefying biomass, while the second step, base-catalyzed liquefaction, featured extensive condensation reactions. By using the developed two-step liquefaction process, the polyols produced from lignocellulosic biomass and crude glycerol containing 26-40% organic impurities showed hydroxyl numbers ranging from 536 to 936 mg KOH/g, viscosities from 20.6 to 28.0 Pa s, and molecular weights (M-w) from 444 to 769 g/mol. The PU foams produced had densities ranging from 0.04 to 0.05 g/cm(3), compressive strengths from 223 to 420 kPa, and thermal conductivities from 32.2 to 38.9 mW/m K. Polyols and PU foams produced from the two-step liquefaction process had improved properties over their analogs derived from a one-step biomass liquefaction by crude glycerol process catalyzed by acid or base. (C) 2014 Elsevier Ltd. All rights reserved.