How to Make Insulated Tumblers

Select two plastic cups that are durable -- not the disposable kind. Be sure that one can sit inside the other, and that there is a small gap between the two on all sides when the rims are at the same level.

Select flexible foam of a thickness that will fit snugly between the two cups when one is inside the other. Cut two pieces of the foam -- one to fit the circle between the bottoms of the stacked cups, and the other to wrap around the outside of the smaller cup, between it and the larger cup. If the two rims are not level, you may need to add more layers of foam between the cup bottoms to bring them to the same height.

Assemble the two cups with the foam pieces snugly between them. You should not need anything to hold them in place other than the friction of the foam against the plastic.

Place the plastic ring -- which should be large enough in diameter and thickness to cover both cup rims -- atop the assembled insulated tumblers. Carefully hot glue the ring in place to hold the cup together and cover any openings between the two. Clean off all excess glue thoroughly. You now have an insulated tumbler.