Put the second ice cube in one paper cup and push the second paper cup inside the first one and down over the ice. Do the same with the third ice cube and the styrofoam cups. Wait for several minutes. The heat from the room causes the ice to melt. Once it has completely melted, check the ice cubes in the cups.
Heat moves from a warmer place to a colder place.
The heat from the room flowed into the ice cube on the plate. That caused the water molecules to warm up and become liquid. To get to the ice cube on the plate, the heat only had to move through air and it does this quickly. The heat cannot move as easily through the paper cup, so the ice cube melted some, but not completely. In the styrofoam cups, the ice melted very little.