The construction industry is highly energy and resource-intensive, contributing to climate change and environmental degradation (Prabhakaran et al., 2020). However, through the implementation of legislative restrictions on organic compound emissions, lightweight sandwich structures developed from natural materials have become a promising approach to enhance both buildings' sustainability and energy efficiency (Prabhakaran et al., 2020). Natural fibres offer an eco-friendlier solution, allowing composites to be produced with lower weight and cost, good mechanical properties, and significantly reduced environmental impact compared to synthetic fibres (Birniwa et al., 2023; Sadeghian et al., 2016). Flax fibres are one of the most promising natural fibres due to their high cellulose content (60 - 80 wt. %), which gives flax fibres inherent stiffness and high strength potential (Perremans et al., 2018). In addition, basalt fibres show great potential to replace synthetic fibres due to higher thermal stability, superior strength and chemical resistance than their glass counterparts (Jamshaid et al., 2016). Moreover, for the production of composite sandwich structures, natural core materials, namely cork, bamboo, coir and hemp, provide several ecological benefits over conventional Polyurethane (PU) and Extruded Polystyrene (XPS) foams (Sadeghian et al., 2016). In this work, composite sandwich panels were developed by using vacuum infusion with natural materials, including bio-based epoxy matrix, flax and/or basalt fibres as reinforcement and cork as core. Therefore, to investigate and select the most suitable solution, the physical, mechanical and thermal properties of the produced panels were evaluated. The results showed that panels using natural materials were successfully produced with target properties for application in the building industry.