The performance of fireproofing materials in providing effective protection from fire strongly depends on the thermophysical properties and on the behavior of the material during fire exposure. Not only active insulators but also nonactive coatings may undergo significant changes in their structure and properties when exposed to high temperatures. The present study focused on the measurement of some key properties for a set of three reference fireproofing materials of different nature. The changes in morphology and in the physical properties during fire exposure were investigated and they were dramatic for the case of active fireproofing materials. For these materials, the time required to reach a steady-state condition in the heat transfer may be significant. The use of a simple heat-transfer model, based on the experimental data obtained for the reference materials studied, demonstrated the importance of accounting for changes in the physical properties, paving the way to further applications in advanced studies of the fireproofing performance in complex geometries and critical scenarios.