Tabs are an extension of the vinyl facing past
the fiber glass blanket. In retrofit this is usually 3” on each side and 6" on one side in new construction. In RetroFit, It is either tucked up along the side of the fiberglass acting as a trim or used to cover the the purlin or girt. An option is to get a factory pre-applied adhesive on the tab, which the installer peels and sticks to the next blanket. This provides a clean seal to the seams and creates a vapor barrier.