Razor Foam is the thinnest sheet foam available, and is a great material for small flies, wing cases on emergers, and stonefly wings like you see on Will Dornan’s Water Walkers series.  You can also sandwich multiple colors together using adhesives such as super 77.  Each package of razor foam comes with two sheets of 0.5 mm and two sheets of 1 mm foam. Each sheet is approximately 1.5 X 4.5.