An insulative panel having a frontside and an opposing backside, and one or more other sides that extend from the frontside to backside, the one or more other sides angling inwardly from the frontside to the backside so that the panel has a tapering profile, the panel being configured to fit into a stud or other such cavity having standardized dimensions, the panel comprising an insulating material with an R-value suitable for use in building construction and remodeling.

A panel structure includes panel members that may be connected together using friction stir welding, Each of the panel members includes a first plate, a second plate substantially in parallel to said first plate, and at least one webbing member connecting the first plate and the second plate. The first plate of the first panel member includes a flange positioned in abutment with a flange located on the first plate of the second panel member. The flange of the first panel member includes a projection and the flange of the second panel member includes a groove. The panel members are connected so that the projection is engaged with the groove to thereby resist relative lateral movement that would separate the panel members.

A panel structure includes panel members that may be connected together using friction stir welding, Each of the panel members includes a first plate, a second plate substantially in parallel to said first plate, and at least one webbing member connecting the first plate and the second plate. The first plate of the first panel member includes a flange positioned in abutment with a flange located on the first plate of the second panel member. The flange of the first panel member includes a projection and the flange of the second panel member includes a groove. The panel members are connected so that the projection is engaged with the groove to thereby resist relative lateral movement that would separate the panel members.

A prefabricated panel building system, including a plurality of wall panels adapted to be joined together; a structural frame defining the shape and configuration of a building; the frame having horizontal tracks wherein the panels are adapted to be slid against each other; each panel including specially adapted interlocking edge members having complementary profiles configured to interlock to form integrated stud or cross members, wherein the arrangement confers substantial rigidity and integrity. A method of building using the panels of the system.