Answer:
Warmboard-S is a structural radiant panel that is 1 1/8" thick, made of Douglas Fir 7 ply plywood, and is sold in full-faced tongue and groove 4' x 8' sheets. Warmboard-R is a radiant panel that is 13/16" thick, made of aspen and pine-oriented strand board (OSB) and is sold in square edged 2'x 4' panels. Warmboard-S is typically used in new construction, while Warmboard-R is most commonly used in remodels. Both products offer the same superior performance.