A substrate is coated on one face with a thin-films stack having reflection properties in the infrared and/or in solar radiation including a single metallic functional layer, based on silver or on a metal alloy containing silver, and two antireflection coatings. The coatings each include at least one dielectric layer. The functional layer is positioned between the two antireflection coatings. At least one of the antireflection coatings includes an intermediate layer including zinc tin oxide SnxZnyOz with a ratio of 0.1≤x/y≤2.4, with 0.75(2x +y)≤z ≤0.95(2x +y) and having a physical thickness of between 2 nm and 25 nm, or even between 2 nm and 12 nm.