Introduction: The maturation process of peloids has been the subject of many studies over time. Knowledge of the processes occurring during this time period, it is very interesting to know the applications of the final product. Material and Method: For preparation of extemporaneous peloids it has been used clay Bentonite Volcangel (Benesa) supplied by Süd Chemie, a mineral water hyperthermal (42°C), sulphurated, weak mineralization (261 mg/l) from Baños Montemayor (M) and water purified obtained by distillation and ion exchange (A).   Peloids were prepared by mixing in the ratio needed aiming to produce a product with 70% water and clay, in polymeric material containers. Water and clay were mixed slowly until total homogenization. The product was introduced into glass containers tightly closed and kept at a constant temperature of 42°C and 8°C.   The percentage of the solid components, water and ashes was determined by gravimetric techniques, drying the sample in oven and muffle furnace (850°C). The specific heat and calorific retentivity were calculated from these data.   　Every six weeks, the analysis of all parameters are repeated in samples maintained at 42°C and 8°C to study possible variations. Results: In Table 1 are shown values of the parameters of the initial peloids prepared with purified water and mineromedicinal water. Conclusion: There were no significant differences observed in the values of the analyzed parameters between the two initial peloids prepared with purified water and with medicinal mineral water of Montemayor spa and a slight diminution in the water percentage, and a small increase of the relaxation time six weeks later.