Flame retardant slabstock polyurethane foam composition

A soft polyurethane foam having a density of 30 to 100 kg/m3 and a flame retardant property,

• wherein the soft polyurethane foam is prepared from a flame retarded slabstock polyurethane foam composition comprising:
• polyol and polyisocyanate as main materials, and an additive for forming a general polyurethane foam except for a flame retarded agent,
• wherein the polyol is polyether polyol and includes 10 to 45 wt % of polyether polyol A having a weight-average molecular weight of 2,000 to 5,000 g/mol and 55 to 90 wt % of polyether polyol B having a weight-average molecular weight of 600 to 1,500 g/mol, and
• an isocyanate index of a range of 70 to 95 as defined by the following equation:
• isocyanate index=amount in moles of isocyanate group (NCO)/amount in moles of hydroxyl group (OH)×100.