Made from softwood fiber, PMDI adhesive, and paraffin, TimberBoard from TimberHP reportedly provides a stable R-3.4 to R-3.75 per inch as above-grade continuous insulation for walls and roofs. According to the manufacturer, the vapor-permeable, nontoxic board allows indoor humidity to escape and balances temperature swings in conditioned spaces to reduce heating and cooling loads. The rigidity of the panels reportedly makes them easy to handle and cut. Available with square or tongue-and-groove edges, the single-ply panels range in thickness from 1 inch to 9 1/4 inches.