For which type of material is the displacement method specifically designed when testing SFRM?

The displacement method in testing Spray-Applied Fire Resistive Materials (SFRM) is specifically designed for lightweight materials, such as polystyrene. This method is particularly relevant when assessing the density of materials with low mass and significant volume stability. Polystyrene, being a lightweight and low-density material, allows the displacement method to be effective, as it requires measuring the volume of water displaced by the sample to determine its density accurately.

Using the displacement method for heavier materials like concrete or steel would not yield the same level of precision or necessity, as these materials are generally tested using other methods that account for their density and other physical properties. Therefore, the focus on polystyrene aligns with the characteristics and practical applications of the displacement testing method in evaluating lightweight SFRM.