Abstract: The invention relates to a transparent substrate, in particular glass substrate, provided with a thin-film stack including at least one metal film with properties in the infrared, in particular a low-emissivity one, arranged between two coatings which each include at least one anti-reflection film based on dielectric material, and at least one protective film based on a sacrificial metal or a partially or fully oxidized sacrificial metal or a sacrificial metal alloy placed between the said metal film and one of the said coatings. According to the invention, the film placed directly below and/or above the said metal film contains at least one of the noble metals Pd, Au, Ir, Pt and Rh. The low-level addition of one or more of these metals to the others, namely the film placed below and/or above the metal film, leads to an increase in the chemical stability and the hardness of the thin-film stack.