<p>Designing and engineering a passenger vehicle suspension requires numerous compromises to maintain adequate levels of passenger comfort, handling and safety. That has been often achieved using sophisticated state-of-the-art suspension technologies, namely, semi-active or fully active suspension systems. However, even the semi-active magnetorheological or valve-based damping systems have maintained their price tags high. Therefore, the demand for an adaptive passive damping technology that would enhance the passive damper performance without the need for expensive electronics has arisen. This work presents a novel concept of a frequency-dependent (FD), passive-adaptive automotive suspension damper. The non-linear dynamic model of the passive twin-tube damper is complemented by the FD valve concept model, verified via experimental tests in a laboratory using a FD damper prototype. In the case of the tested prototype, rebound damping forces at medium and high frequencies were reduced down to 68% compared to the base damping force at low frequencies while the basic damping function was maintained when operating within the low speed/low frequency range of the excitation inputs. Thus, the proposed solution may contribute to improving passenger comfort while maintaining good steering response and body control of a vehicle. The presented FD damper effectively fits in between conventional passive dampers and state-of-the-art semi-active systems, while maintaining a price tag approaching the former. The presented concept may be a significant aid in designing FD valves, not only for the automotive industry.</p>