Rigid polyurethane foams

Process for making rigid polyurethane or urethane-modified polyisocyanurate foams comprising:

• reacting an organic polyisocyanate composition with an isocyanate reactive composition in the presence of
• a blowing agent;
• 0.05-5 wt %, relative to the weight of the isocyanate reactive composition, of a first tertiary amine catalyst;
• and
• 0.01-5 wt %, relative to the weight of the isocyanate reactive composition, of a second tertiary amine catalyst;
• wherein said first catalyst is selected from the group consisting of 2,2′-dimorpholinodiethylether, 1-methylimidazole, and 4-dimethylaminopyridine,
• wherein said second catalyst has a pKa above 12,
• and
• wherein said isocyanate reactive composition comprises, relative to the total weight of isocyanate-reactive compounds, at least 10 wt % of polyester polyol.