Flexible Polyurethane Foam

A method of forming a flexible polyurethane foam, said method comprising the steps of:

• providing a polyisocyanate composition comprising;
• a polymeric diphenylmethane diisocyanate (MDI) component;
• and
• a monomeric diphenylmethane diisocyanate (MDI) component comprising 2,4′-MDI;
• wherein the 2,4′-MDI is present in the monomeric MDI component in an amount greater than 35 parts by weight of the 2,4′-MDI based on 100 parts by weight of the monomeric MDI component;
• providing an isocyanate-reactive composition comprising;
• a primary hydroxyl-terminated graft polyether polyol comprising a carrier polyol and particles of co-polymerized styrene and acrylonitrile dispersed in the carrier polyol, wherein the carrier polyol has a weight average molecular weight of greater than or equal to 3,500 g/mol;
• a second polyol different from the primary hydroxyl-terminated graft polyether polyol;
• and
• reacting the polyisocyanate composition with the isocyanate-reactive composition to form the flexible polyurethane foam;
• wherein the flexible polyurethane foam exhibits flame retardance under a flammability test according to California Technical Bulletin 117 regulations irrespective of an amount of flex fatigue of the flexible polyurethane foam.