Under ballast mats (UBM) have demonstrated their capacity to reduce section stiffness and ballast degradation. However, UBM can cause ballast destabilisation under some circumstances due to excessive vertical track deflections, requiring the installation of geogrids over the mat which increases costs and time. As alternative to this solution, this paper shows the design of GridMat: a sustainable technology for ballasted railways that combines the concepts of geogrids and under ballast mats (UBM) manufactured from recycled crumb rubber. This aims to provide damping capacity while limiting the oscillations and settlement of ballast layer. To obtain the optimal GridMat design, five different configurations varying the aperture size and void areas were assessed through laboratory box tests reproducing the track section including the GridMat. Results showed that the optimal Gridmat was of 55 mm aperture seize and 25% void area. To evaluate the sustainability of this design, the expected number of conservation and renewal operations were calculated from full-scale laboratory tests and a life-cycle assessment and life-cycle cost analysis were undertaken. GridMat showed long-term reduction in ballast degradation and track settlement, reducing need for maintenance and renewal operations in comparison with standard mats.