Insulated Plastic Coffee Cups

Insulating Container?

I have a project tin school. My project is to build the best insulation container I can. Currently, I have a a plastic container. In that plastic container is a starbucks Coffee cup. In between the large gap between the cup, and the plastic container, I have polyester fiberfill. Are there any ways to improve the insulation of this container?

1/4″ of air has more “R” value than fiberglass but after a thickness of .375″ it has a thermal breakdown and flows like the weather. Use layers of insulation separated by air.
The ‘R” value of insulation if you take it’s reciprical (1/R=U)
gives a U value which is the amount of btu’s/hour times the square foot times the difference in tempF that will either leave or enter through that substance.