"Mimetic" molecular composites can be viewed as hybrids of conventional and "molecular" composites, and are prepared from a matrix and reinforcing fiber consisting of a single polymer composition. The aim of the work was to obtain a good chemical, physical and thermal property match at the interface for an overall excellent balance of composite properties. Kevlar(R) aramid 49/poly(p-phenylenelerphthalamide. an all-PPD-T-dagger composite. was used as a model system in the work, and, in theory, should be ideal for testing the merit of the "mimetic" molecular composite concept. The key to the successful preparation of all-PPD-T infusible composites was the acid catalyzed thermal transformation of a fusible precursor, poly(N,N＇-di-sec-butyl-p-phenyleneterephthalamide), into PPD-T. The composites were prepared by embedding Kevlar(R) aramid 49 fibers in poly(N,N＇-di-sec-butyl-p-phenyleneterephthalamide) resin, which, on heating in the presence of benzene sulfonic acid catalyst, dealkylated to a PPD-T matrix. In this way, Kevlar(R) aramid 49/PPD-T(8/92 to 40/60 v/o) composites with densities in the range of 0.2 to 1.2 g cm(-3) (versus similar to 1.4 g cm(-3) for a fully consolidated PPD-T composite) have been prepared and their thermal and mechanical properties characterized. Some of the foamed composites prepared in this work bear a remarkable resemblance to wood, a natural fiber reinforced foam composite, but with the advantages of flame and rot resistance.