Comfortboard CIS (Commercial Insulated Sheathing) is a non-combustible stone-wool insulation board designed for use as exterior continuous insulation in rainscreen wall systems. The manufacturer says that it repels water but is breathable enough to allow outward wall drying. Available in several thicknesses; the 1 1/4-inch version costs 80 cents per square foot. Roxul Insulation, 905.878.8474, roxul.com
