The present invention relates to multi-layer fiber products and a method of manufacturing these kinds of products. The present product comprises a first layer (12) consists mainly of natural fibers and a second, heat-sealing layer (14) located on top of the first layer. The heat-sealing layer (14) consists mainly of synthetic thermoplastic fibers or particles. According to the present method, the heat-sealing layer (14) is brought onto the first layer (12) already during the web forming process, the first and the second layers being formed and joined together in a foam forming process. With the present invention, it is possible to decrease the amount of plastic materials in packaging materials having heat-sealing properties.