A sleeve for jacketing a container such as a beverage cup, where the sleeve is assembled by cutting and folding from a unitary flat panel, the sleeve having no outwardly projecting flaps or ridges. Inwardly folding flaps adapt themselves to the taper and diameter of the cup. Multiple layers of material thickness in the sleeve may be realized using the templates and folding methods of the invention, and the sleeve is printable on either or both sides so that decorative or commercial indicia may be displayed according to the end user's needs or wishes. The invention finds use in making printed insulative sleeves having logos and other customized indicia, and may be folded according to the methods of the invention by the supplier or by the user of the sleeve.