My son in grade 5 had to do an experiment to make insulated cups using different materials. He made one using insulated Styrofoam pieces from ripped up cups and one using cotton balls. He packed Styrofoam pieces into a large cup and placed a smaller cup inside the larger cup and packed more Styrofoam between the small cup and the large cup. He did the same with 2 other cups and cotton balls. He then poured equal amounts of water into each cup and placed them in the freezer and timed how long it took for the cups to completely freeze. The one that seemed to work the best was the cotton ball cup (i.e. it took the longest to freeze). But, he has to explain why? Is it because it is easier to pack cotton balls than Styrofoam (i.e. less air gets in around the outside edge of the Styrofoam cup)?