The present invention is directed to a process for preparing water-blown rigid polyurethane foams having at least an 80% closed-cell content which involves reacting a) at least one polyol mixture which is composed of (i) at least one polymer polyol; (ii) at least one polyol having a hydroxyl value within the range of from about 200 to about 800; and (iii) optionally, at least one polyol having a hydroxyl value within the range of from about 25 to about 115; with b) at least one polymeric isocyanate and/or a prepolymer thereof; in the presence of c) optionally, at least one catalyst; d) water; and e) optionally, at least one additive or auxiliary agent. The present invention is also directed to the closed-cell water blown rigid polyurethane foams produced by the process of the present invention. The invention is further directed to a polyurethane-foam forming mixture which is used to produce the water-blown rigid polyurethane foams of the present invention. Foams produced according to the present invention have reduced friability and acceptable adhesion to substrates as well as acceptable compressive strength.