Metal threads consist of metal strips, primarily gold, gold alloys, silver, copper or aluminium, wound around a fibrous core of linen, cotton, silk or other yarns. Metal threads are extensively used for the decoration of different clothing and decoration accessories in Churches and Palaces in Spain. Nowadays, they are widely used in Holly Week celebrations in Spain, providing a wide variety of such species for their characterization and determination of their origin and manufacturing processes. In this work, it is reported that thermal analysis techniques, mainly differential thermal analysis (DTA) and thermogravimetric analysis (TGA) are very useful to evaluate metals threads. The obtained results were confirmed by other experimental techniques, mainly Scanning Electron Microscopy and Energy Dispersive X-Rays. The thermal decomposition of the threads is affected by the fibre type, the metallic components, the possible metal corrosion and the thermal experimental conditions, primarily the atmosphere (experiments were carried out in N2 and air atmosphere). The presence of silk and cotton in the threads has been determined by thermal analysis. The study of the different natural fibres showed a mass loss and an endothermic effect at low temperature followed by other thermal effects at higher temperature attributed to the degradation of the organic fibre compounds. In this study, important differences have been observed in the DTG curves between vegetal and animal fibres. Thus, the maximum temperature of the DTG peaks appears at 300ºC for silk and wool and at 350ºC for cotton and linen. Cotton and linen a.re marked by an exothermic degradation at about 350 ºC, whereas silk undergoes an endothermic degradation. Samples containing copper show an increase in mass in the range between 560 and 900 ºC when heating in air atmosphere that is not shown under inert N2 atmosphere. This weight increase is attributed to the oxidation of metallic copper to copper (II) oxides. The decomposition of the fibres is also attributed to the presence of copper. The aluminium metal is responsible of the endothermic peak shown at ca. 660 ºC in the DTA curve (melting point of aluminium). The presence of silver is detected in DTA curve by a peak at 962 ºC) (melting point of silver). The corrosion compounds have been also detected by thermal study, i.e. samples with high content in silver chloride produced by corrosion show an important mass loss in the TG curve attributed to decomposition of this salt. The treatment of the metallic treads with organic compounds used to preserve from corrosion or for pasting to the others components show mass loss and exothermic effect that facility its characterization.