Advanced structural components comprising a foamed thermoplastic that can be used in virtually any application where wooden components have a use. Such structural components can comprise sized lumber, shaped trim, posts, beams or shaped structural members. An advanced profile composite structural component comprising an exterior capping layer with an interior comprising a foamed thermoplastic can be used in the assembly of fenestration units adapted to residential and commercial structures. Preferably the profile structural component can be used in a window or door assembly. The profile member is adapted for ease of construction of the fenestration units, can be easily installed in a rough opening to framing members, and can be trimmed and adjusted on site. The profile is structurally strong, thermally stable, shrink resistant and will accept and retain the insertion of fasteners such as staples, nails and screws permanently with substantial retention and little or no damage to the units. The profile structural components possess strength that permits the manufacture of a structurally sound fenestration unit from two or more foamed profile members or other conventional members.