What cup would you use to keep a drink cold?
use a metal container to keep a drink very full
A Styrofoam cup will do both. The Styrofoam is an insulator, and, as such, it slows the transfer of heat between the system (the drink) and the surroundings (everything outside the cup) If it is a cold drink, heat moves very slowly through the cup toward the drink. If it is a hot drink, heat moves very slowly through the cup toward the surrounding air.