Formal evening dresses usually come down to a combination of fabric, structure and finish. Fabrics like satin, mesh, lace, chiffon, sequins or draped jersey naturally feel more occasion-focused because they catch light, create movement or hold shape differently than casual fabrics like cotton or denim. Details also make a difference with features like open backs, corset-style bodices, ruching, floor-length hems or elevated draping instantly shift the look into more formal territory.