This strong, smooth, lightweight pale blue-gray material is the ultimate in corrugated boards. Available in either single wall (approx. 0.125'') or double wall (approx. 0.25'') thickness, Perma/Dur Corrugated Board is acid-free, lignin-free and alkaline buffered with 3% calcium carbonate added for an alkaline reserve in all three layers for maximum protection. This exclusive board is made of fully bleached virgin fibers and is unusually strong - an excellent choice for boxmaking, print backers, picture framing, dividers - wherever a sturdy, light board is required.