A substantial portion of the existing building stock is highly vulnerable to seismic forces, as many structures were built without accounting for horizontal loads. This vulnerability was starkly highlighted by recent earthquakes in Italy and across Europe. In addition to their seismic deficiencies, these older buildings often suffer from significant energy inefficiencies due to the use of materials with poor mechanical and thermal performances, as well as the presence of thermal bridges that lead to energy loss. To address these dual challenges, innovative construction techniques have emerged, offering solutions that improve both seismic resilience and energy efficiency. One effective approach is the use of integrated seismic-energy coating systems, which are minimally invasive and externally applied to the building envelope. This paper presents an experimental study carried out at the National Institute for Research and Development in Constructions (INCERC) in Timișoara (Romania), focusing on a masonry panel retrofitted with the MIL15.s system, developed by the Italian company TM Group S.r.l. The retrofitting technique employs a lightweight metal exoskeleton made of extruded aluminium alloy profiles combined with sandwich panels to enhance both mechanical and thermal performance. The experimental campaign focused on the evaluation of the panel’s behaviour under out-of-plane seismic actions. The findings demonstrate the potential of the MIL15.s system to significantly enhance out-of-plane performance while contributing to energy efficiency, thus laying the groundwork for future testing and full-system validation.