Designed for use with radiant-heat floor systems under tile, the Hottrok Tile Mat has both thermal and acoustic insulating properties and can be installed over most wood and concrete substrates that meet TCNA standards. Grooves in the mat hold, support, and protect cables until they are covered with mesh and leveler. The 1/2-inch-thick molded polypropylene foam material is resistant to alkalies and acids and highly resistant to humidity and water, according to Hottrok. Mats have an R-value of 1 and retail at $39 per 2-foot-by-3-foot sheet.