Made from extruded polystyrene, a closed-cell foam, this board is completely waterproof, front to back. For performance integrity, ProPannel tile backerboard should be installed using proprietary nails, washers, and mastic on all penetrations and seams. The Portland cement­based face coating is reinforced with fiberglass mesh and provides a base for thinset adhesive application. The manufacturer states that its board is suitable for use on shower walls as well as under floor tile, having passed the Robinson Floor Test for light commercial applications. The panel measures 3x5 feet x 1/2 inch, weighs 8.67 pounds, and cuts easily with a standard utility knife. The board lists for about $1.25 per square foot.

W.R. Bonsal, 800/738-1621, www.bonsal.com.

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