<p>A computational formulation has been proposed for the thermo-structural analysis of multiple composite layers incorporating ablative materials for passive thermal protection systems. This formulation is based on the semi-analytical finite element method and includes user subroutines to model the progressive decomposition of pyrolyzing materials accurately. Material properties are evaluated through specimen testing, and the design parameters for the composite layers are determined using the proposed formulation, together with the specimen test results. Additionally, the detailed thermo-structural performance of these layers is investigated using 3D finite element analysis. The results are compiled to provide insights into the thermo-structural characteristics of composite layers with ablative materials used in passive thermal protection systems.</p>