Test results are presented for a matrix type phase change thermal storage tile module with no surface covering, intended to transfer heat directly to and from room air at small temperature differences. Heat is stored and released by melting and freezing mixtures of fatty acids, which constitute up to half the weight of the tile. The polymeric matrices tested were powders or granules of poly(vinyl chloride) (PVC), poly (vinyl acetate) (PVAc), poly(vinyl alcohol) (PVA), vinyl acetate‐vinyl chloride copolymer (VAc‐VC), and high density polyethylene (HDPE). The tiles keep their shape and dimensions without any weeping of liquid fatty acid, up to 37 or 51°C, depending on their composition. In the case of PVC and PVA, infrared spectra and differential scanning calorimetry indicate interactions between the polymer and the fatty acids, which may increase the surface tension and allow larger matrix pores before weeping begins. Some of the tiles were reinforced with glass fibers, and others with cellulose fibers. The best mechanical properties were obtained with 5 percent of long (85 to110 mm) glass fibers. Paraffin chloride and antimony trioxide served as satisfactory fire retardants.