One piece molded roof for a vehicle cab and method of molding the roof

A one piece rotational molded roof for a vehicle cab is provided in which separate inlet ducts (20) and outlet air ducts (34) are molded in the roof. The ducts (20, 34) are formed by molding upper and lower panels (14, 16) that are widely spaced to form the ducts (20, 34) and which are closely spaced about the periphery of the ducts (20, 34). After a solid surface layer is molded, a second resin charge containing a foaming agent is dropped in the mold. This resin coats interior of the solid surface layer and later foams. The foam expands and extends completely between the closely spaced upper and lower panels of the solid surface layer to seal between the inlet and outlet air ducts (20, 34). The foam is rigid to strengthen the roof.