NOVELTY - The facet has a front reflective layer (1) made of float monolithic glass for reflecting solar radiation, and a rear supporting layer (3) made of a thermoplastic loaded with fiberglass, where result of multiplying Young's modulus value of the rear supporting layer by the inertia value in axes defining the plane of the rear supporting layer is equal to the result of multiplying the Young's modulus value of the front reflective layer by the inertia value in the axes defining the plane of the front reflective layer, and thermal expansion coefficients of both the front and rear layers are equal.    USE - Sandwich-type facet for a heliostat (claimed) for use in solar field for generation of power.    ADVANTAGE - The result of multiplying Young's modulus value of the rear supporting layer by the inertia value in axes defining the plane of the rear supporting layer is equal to the result of multiplying the Young's modulus value of the front reflective layer by the inertia value in the axes defining the plane of the front reflective layer, and thermal expansion coefficients of both the front and rear layers are equal, thus maintaining geometry at any temperature range by providing balanced design, reducing weight, enabling separation of tensional elements in thermal dilation, controlling temperature differences between the reflecting mirror and the rear support layer during the injection of the intermediate layer to provide high precision curvature, allowing different curvatures along the main axis and with homogeneity in density, providing flexibility in the polymer foam intermediate layer thickness, controlling geometry in facets with a low curvature (large radius) for use in large-scale stations, enabling flexibility in the control of different curvatures in both axes to permit round, parabolic or cylindrical facets, and ensuring high precision optical behavior. The rear supporting layer includes fiber cement to properly adjust the coefficient of the rear support to be matched to that of the front layer, or slightly modified compensating differences in temperature during operation in the rear of the front glass which absorbs small part of the radiation while the rear support stays in shadow, to control the rear support composition and the hygroscopic dimensional variation through water-proof type treatments, to provide UV radiation resistance, to allow to drill and install the facet within the interface of the heliostat structure easily, and to reduce the weight per side, thus reducing structural costs of the heliostat while enabling easy handling and transportation of the facet.    DETAILED DESCRIPTION - The rear supporting layer comprises fiber cement i.e. Portland-type cement, that includes minerals, natural fibers and/or binder additives. An INDEPENDENT CLAIM is also included for a method for manufacturing a facet.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross section view of a sandwich-type heliostat facet.    Front reflective layer (1)    Intermediate polymer foam layer (2)    Rear supporting layer (3)    Fiberglass reinforcement layer (13)