Abstract: It is therefore the object of this invention to provide prefabricated insulation sheets, to fit around specific-sized perimeters of duct, which includes methods for anchoring sheets to surface to which they are applied, sealing jacket overlaps to adjacent jackets, and attaching overlapping longitudinal ends of sheets. This prefabrication replaces job-site cutting-to-length of sheets with flanges, as well as the additional step of sealing the exterior of jacket laps after installation, and the attachment of longitudinal ends of sheets with staples. It also provides a method of anchoring the end of sheets to the surface to which they are applied. The invention thereby both improves the installation method and the effectiveness of the attachment thereby improving productivity, reducing costs, and increasing the quality of the installation.