Abstract <p>To achieve a lower onset isolation frequency and reduced resonance response amplitude, while minimizing the deterioration of high-frequency isolation performance, this study proposes a novel integrated passive isolator. By exploiting the nonlinear benefits of an X-structure, the proposed system achieves low-friction and low-resonance (LFLR) vibration isolation through the synergistic integration of nonlinear stiffness, damping, and inertia. The design incorporates a compact stiffness-tuning mechanism, enabling an extensive quasi-zero-stiffness (QZS) range—up to 49.09% of the allowable vibration displacement—while supporting substantial payloads (demonstrated at ~ 4&#xa0;kg, with scalability to arbitrary loads). This configuration delivers exceptionally low resonant frequencies (0.69&#xa0;Hz) and isolation onset at 1.2&#xa0;Hz, outperforming comparable solutions reported in the literature. A frictionless eddy current damper (ECD) further enhances beneficial nonlinear damping performance by eliminating Coulomb friction inherent in fluid-based systems, reducing resonant amplitude to ~ 7&#xa0;dB (e.g., <i>θ</i>₀ = π/3) and achieving superior high-frequency isolation (transmissibility around − 35&#xa0;dB at 10&#xa0;Hz). Additionally, a novel nonlinear inertia mechanism allows significant inertial mass variation during large-amplitude oscillations without imposing motion constraints, introducing the mass variation ratio as a key metric for optimizing inertial effects. Collectively, these innovations underscore the versatility and adaptability of the integrated X-structure approach for advanced vibration control applications in engineering practice.</p> Graphical abstract <p></p>