A substrate is coated on one face with a thin-film multilayer including at least one functional metal film based on silver or made of silver having a thickness e of between 7 nm and 20 nm inclusive of these values, and two antireflection coatings each including at least one antireflection film. The functional film is placed between the two antireflection coatings. The multilayer includes a lower discontinuous metal film having a thickness e′ of between 0.5 nm and 5 nm inclusive of these values. The lower discontinuous metal film is located between the face and the only or first functional metal film as counted starting from the face.