A quantitative photoacoustic (PA) phase theory for multilayer materials has been developed by using the surface temperature approach, and experimentally confirmed with the step-scan Fourier transform infrared PA phase data of multilayer polymer samples. This theory unifies several previous PA phase theories for specific cases and provides a clear picture of the relationship between the PA phase response of each layer and the thermal, optical, and geometric properties of a multilayer sample. Within the context of this model, it is shown how the PA phase difference is easily obtainable and instrument independent, and thus widely applicable to spectral depth profiling of multilayer materials. The theory can be readily applied to either qualitative discrimination of PA signals from different layers, or quantitative determination of the thermal diffusivities, optical absorption coefficients, or thickness of different layers. © 1995 American Institute of Physics.