A combination of cellulose fibers and cementitious materials, HardiePlank is fiber-cement siding that comes in long, horizontal strips, just like wood lap siding. HardiePlank is partly wood, in the form of cellulose, and partly mineral. Break a piece of HardiePlank, and inside you will see a brittle core interlaced with wood fibers.
HardiePlank’s wood content does not influence its distinctive wood grain appearance. That is the result of embossed texturing. HardiePlank’s embossing serves two purposes. First, it does create a reasonable simulation of wood grain. Second and most importantly, the embossing visually breaks up the flat surfaces and gives each board a richer look. James Hardie Industries does offer a smooth texture, too.
HardiePlank is not to be confused with HardiePanel, also produced by James Hardie Industries. HardiePanel, also composed of fiber-cement, is the tall, vertical version of HardiePlank, at 48 inches wide by 96 inches to 120 inches long.