Sixteen brass leaves, or petals, form the outer surface of the mug. They are aligned vertically, like planks of wood forming a barrel. Each one is hinged near the top, just below the solid rim for drinking from. Enclosed between each leaf and the inner mug is a wax-filled piston, attached to the base of the mug and to somewhere just under the hinge of the petal.
The wax in the pistons is chosen to have a phase change at drinking temperature. If the liquid is warmer than that, the petals gently unfold and form a heat-radiating flower shape. When the liquid has cooled sufficiently, the petals fold in tightly and trap a layer of air around the mug, insulating it.