A shell apparatus to enhance insulation and prevent air transmission of an electrical junction box coupled to a stud is provided. The electrical junction box includes at least one wire coupled to a housing member and positioned within a wall cavity between a front wall and rear wall. The housing member of the electrical junction box includes an opening aligned with an opening in the front wall. The shell apparatus includes a foldable sheet with a center portion, a first flap, a second flap, and a third flap. The first and second flaps are coupled to the stud, and the third flap is coupled to the rear wall to permit the foldable sheet to enclose the electrical junction box's housing. An expansion foam is disposed between the foldable sheet and electrical junction box to entirely fill the void between the front wall, rear wall, foldable sheet and electrical junction box.