Representative samples of four spray-applied FRMs were obtained from two of the largest manufacturers in the industry. Two of the materials are mainly composed of mineral fibers with a portland-cement based binder. The other two are gypsum-based with either vermiculite or expanded polystyrene beads as lightweight extenders. In the sections that follow, the materials will be identified only by their binder components, portland cement and gypsum, respectively. Two of the materials (one portland cement-based and one gypsum-based) are currently available in the U.S. marketplace, while the other two were of interest for historical reasons and are still in use in various existing structures. In the latter case, the materials were supplied by the manufacturers in a condition that matched the historical materials as closely as possible. Samples of both of the portland cement-based and one of the gypsum-based materials were sent to a commercial testing laboratory for evaluation of thermal conductivity, heat capacity, and density (via mass and thermal expansion measurements). 1 In addition, the materials were characterized by thermogravimetric, dimensional, differential scanning calorimetry, and optical microscopy analysis in the NIST labs.