Poly Mesh (breathable) underbelly is Standard.
Aluminum underbelly is an available option, and should be
considered if large rodents are a problem for your area.
R-12 insulation (solid roll below the joists) is standard in the floor.
Fiberglass insulated ductwork is standard. Our competition uses less expensive (cheaper) metal ductwork that is noisy and not sealed as well as our insulated work. Losing heat and A/C from your ductwork is certainly not energy efficient.