You need to reduce heat flow between the cup
and the room. Cover the cup with two layers of clear plastic to keep the
water from contact with room air. Hold the plastic on with a rubber band.
Use a Styrofoam cup to reduce heat flow through the sides. (Styrofoam cuts
down on heat flow; it is a bad thermal conductor.) If a Styrofoam cup of
the right size is not available, wrap your cup with several layers of dry
paper towels.
