Written by the late great John Addington, styleatollah at the Star Tribune:
There is no such thing as a Styrofoam cup, or Styrofoam picnic cooler, or egg carton, or picnic plate. Dow Chemical Co. patiently informs us of this each time we use the trademark incorrectly, or when we use the word uncapped. Styrofoam is used in insulation, in buoyancy billets for boats and in decorative board. It is never used in consumer products. To be entirely proper we should just say plastic foam cup or whatever.