Abstract: A method of producing a closed-cell and rigid foam. The method comprises reacting an isocyanate composition including one or more polyisocyanates and a polyol composition including one or more polyols including one or more aromatic polyester polyols having a hydroxyl functionality of greater than 2 and one or more physical and/or chemical blowing agents including methylal to form a closed-cell and rigid foam configured to retain at least 85% of an initial volume of the closed-cell and rigid foam when exposed to about 97% relative humidity at about 70° C. for at least seven or more days.