Methods and apparatus for eliminating or reducing a surface skin when producing a flexible polyurethane foam slab are disclosed. The top surface of the chemically reactive polyurethane foaming mixture is heated during and/or after the foaming mixture expands. The heating preferably is conducted so as to prevent a significant temperature gradient from forming between the internal temperature of the foaming mixture and the top surface of that mixture. Preferably, heat is applied so as to heat from the top surface of the foaming mixture in an escalating fashion to higher temperatures as the foam is conveyed along a conveying path away from the foaming mixture dispensing device.