Method for manufacturing an article of underwear, in particular a bra, comprising the steps of: - providing a first fabric layer, designed to realize the outer layer of the underwear article, cut according to a shape substantially corresponding to the plane projection of the stretched underwear article; - providing a second fabric layer, designed to realize the inner layer of the underwear article, cut according to a shape substantially corresponding to the plane projection of the stretched underwear article; - providing a third film material, designed to realize permanent joining elements between the first fabric layer and the second fabric layer in the finished underwear article, said third film material being cut to form at least one central underbreast portion, a pair of upper portions (19, 19') destined to be arranged in correspondence of the bra shoulder straps and a pair of side portions (20, 20') destined to be arranged in correspondence of the sides of the bra, and said third film material being a "silicone-free" thermo-adhesive polyurethane film; - sprinkling said first fabric layer, on its side destined to face the second fabric layer, with a reactive "hotmelt" polyurethane glue, capable of being reactivated only once, by heating, within a reactivation period of time of at least 3 days from the application, preferably within 5 days from the application; - applying the aforesaid thermo-adhesive polyurethane film portions (18, 19, 19', 20, 20') in position on the side of the second fabric layer destined to face the first fabric layer and to heat-seal said portions on said second fabric layer by hot pressing; - superimposing said first and second fabric layers (11, 13), with the side of the first fabric layer covered with reactive polyurethane glue faced towards the second fabric layer and the thermo-adhesive polyurethane film portions (18, 19, 19', 20, 20') applied to the second fabric layer facing the first fabric layer; - within said reactivation period of the reactive "hotmelt" polyurethane glue, joining, by hot-pressing, the two layers of fabric (11, 13) cut according to the respective shapes (12, 14), with the aforesaid thermo-adhesive polyurethane film portions (18, 19, 19', 20, 20') interposed between them, reactivating the reactive polyurethane glue to bring it temporarily into a liquid phase, suitable for penetrating through the fibres of the fabrics to be joined, and subsequently triggering a chemical cross-linking process to solidify it definitively for the definitive and permanent fixing of the parts; - at the end of the cross-linking process of the polyurethane glue, thermoforming the underwear article according to the desired shape; - applying shoulder straps, hooks, labels and other possible accessories for the final completion of the underwear article. - providing a first fabric layer, designed to realize the outer layer of the underwear article, cut according to a shape substantially corresponding to the plane projection of the stretched underwear article; - providing a second fabric layer, designed to realize the inner layer of the underwear article, cut according to a shape substantially corresponding to the plane projection of the stretched underwear article; - providing a third film material, designed to realize permanent joining elements between the first fabric layer and the second fabric layer in the finished underwear article, said third film material being cut to form at least one central underbreast portion, a pair of upper portions (19, 19') destined to be arranged in correspondence of the bra shoulder straps and a pair of side portions (20, 20') destined to be arranged in correspondence of the sides of the bra, and said third film material being a "silicone-free" thermo-adhesive polyurethane film; - sprinkling said first fabric layer, on its side destined to face the second fabric layer, with a reactive "hotmelt" polyurethane glue, capable of being reactivated only once, by heating, within a reactivation period of time of at least 3 days from the application, preferably within 5 days from the application; - applying the aforesaid thermo-adhesive polyurethane film portions (18, 19, 19', 20, 20') in position on the side of the second fabric layer destined to face the first fabric layer and to heat-seal said portions on said second fabric layer by hot pressing; - superimposing said first and second fabric layers (11, 13), with the side of the first fabric layer covered with reactive polyurethane glue faced towards the second fabric layer and the thermo-adhesive polyurethane film portions (18, 19, 19', 20, 20') applied to the second fabric layer facing the first fabric layer; - within said reactivation period of the reactive "hotmelt" polyurethane glue, joining, by hot-pressing, the two layers of fabric (11, 13) cut according to the respective shapes (12, 14), with the aforesaid thermo-adhesive polyurethane film portions (18, 19, 19', 20, 20') interposed between them, reactivating the reactive polyurethane glue to bring it temporarily into a liquid phase, suitable for penetrating through the fibres of the fabrics to be joined, and subsequently triggering a chemical cross-linking process to solidify it definitively for the definitive and permanent fixing of the parts; - at the end of the cross-linking process of the polyurethane glue, thermoforming the underwear article according to the desired shape; - applying shoulder straps, hooks, labels and other possible accessories for the final completion of the underwear article.