A method for manufacturing an under sleeper pad comprising a supporting wall having a bearing face and on its opposite side a securing face provided with a distribution of endogenous coupling relief elements - projections, recesses - capable, the pad being in its final general configuration and in the solid state, of being embedded in a securing face of a sleeper of concrete or the like having a supporting face on its opposite side, such a coupling relief element comprising a proximal narrow portion towards the securing face, a distal enlarged portion, and one or more facets extending parallel to or inclined with respect to the securing face, wherein: - a pad plate molding means having a certain rigidity is provided, comprising a peripheral side wall and a mold shaping face comprising a distribution of mold relief elements - projections, recesses -, forming a mold cavity adapted to be filled with the constituent material of the pad, the shape of the mold cavity corresponding - in a complementary manner - with that of the pad to be created, the distribution of mold relief elements being in correspondence - in a complementary manner - with the distribution of coupling relief elements, a mold relief element comprising a proximal narrow portion, a distal enlarged portion, and one or more facets extending parallel to or inclined with respect to the mold shaping face, - polymeric material is provided, in particular thermoset polyurethane elastomer, able to be brought: • first to a fluid state for the purposes of molding, • to a solid state in order in order to associate the demolded pad with the concrete or similar of the sleeper, • and to a deformable state in which it has a capacity for temporary local and at least substantially elastic deformation, - the polymeric material is brought to said fluid state and the mold cavity of the pad plate molding means is filled with it for the purposes of molding the pad plate, - at a later stage, the polymeric material is brought to said deformable state, - and, while the polymeric material is in the deformable state, a relative extraction force is exerted on the previously molded pad plate relative to the pad plate molding means, such that its coupling relief elements are elastically and temporarily deformed in said deformable state so as to detach the mold relief elements, thereby permitting the demolding of the pad plate, - then, the pad constituted by or coming from the pad plate is provided in the general configuration which is its final general configuration when the polymeric material is in said solid state. - a pad plate molding means having a certain rigidity is provided, comprising a peripheral side wall and a mold shaping face comprising a distribution of mold relief elements - projections, recesses -, forming a mold cavity adapted to be filled with the constituent material of the pad, the shape of the mold cavity corresponding - in a complementary manner - with that of the pad to be created, the distribution of mold relief elements being in correspondence - in a complementary manner - with the distribution of coupling relief elements, a mold relief element comprising a proximal narrow portion, a distal enlarged portion, and one or more facets extending parallel to or inclined with respect to the mold shaping face, - polymeric material is provided, in particular thermoset polyurethane elastomer, able to be brought: • first to a fluid state for the purposes of molding, • to a solid state in order in order to associate the demolded pad with the concrete or similar of the sleeper, • and to a deformable state in which it has a capacity for temporary local and at least substantially elastic deformation, • first to a fluid state for the purposes of molding, • to a solid state in order in order to associate the demolded pad with the concrete or similar of the sleeper, • and to a deformable state in which it has a capacity for temporary local and at least substantially elastic deformation, - the polymeric material is brought to said fluid state and the mold cavity of the pad plate molding means is filled with it for the purposes of molding the pad plate, - at a later stage, the polymeric material is brought to said deformable state, - and, while the polymeric material is in the deformable state, a relative extraction force is exerted on the previously molded pad plate relative to the pad plate molding means, such that its coupling relief elements are elastically and temporarily deformed in said deformable state so as to detach the mold relief elements, thereby permitting the demolding of the pad plate, - then, the pad constituted by or coming from the pad plate is provided in the general configuration which is its final general configuration when the polymeric material is in said solid state.