Which cup insulation works best and why?

i recently conducted a science prac on this one, and i found that the foam cup was the best, followed by plastic, then the mug and a glass cup. However the results were quite close, about 2 or 3 degrees celcius difference so it wont really matter which cup you use, just as long as it keeps your tea or coffee hot :P

Insulators stop heat flowing through them by either using air pockets (such as, in this case, the foam cup) or by their molecular structures being organised unlike metals, which have free electrons that aid the passage of energy.