Polyurethane rigid foam

A foam-forming composition for producing a polyurethane rigid molded foam article for making structural construction materials, the foam-forming composition comprising:

• (a) at least one isocyanate component;
• and
• (b) at least one isocyanate-reactive component comprising an isocyanate-reactive composition including:
• (bi) a rigid polyol blend having a nominal hydroxyl functionality from 3 to 10 and a hydroxyl number from 125 mg KOH/g to 800 mg KOH/g, the the rigid polyol blend comprising at least the following:
• (bi1) a first rigid polyether polyol having a nominal hydroxyl functionality of 5 and a hydroxyl number from 300 mg KOH/g to 450 mg KOH/g,
• (bi2) a second rigid polyether polyol having a nominal hydroxyl functionality of 7 and a hydroxyl number from 300 mg KOH/g to 450 mg KOH/g, and
• (bi3) a third rigid polyether polyol having a nominal hydroxyl functionality of 3 and a hydroxyl number from 600 mg KOH/g to 800 mg KOH/g;
• and
• (bii) at least one flexible polyol compound having a nominal hydroxyl functionality from 2 to 3 and having a hydroxyl number from 20 mg KOH/g to 100 mg KOH/g;
• (c) a catalyst package comprising at least one latent gelling catalyst;
• and
• (d) at least one blowing agent;
• wherein an isocyanate index of the foam-forming composition is from 90 to 400 and the polyurethane rigid molded foam article has a molded foam density of from 100 kg/m3 to 1000 kg/m3 according to ASTM D1622.