The use of recycled and renewable components in structural applications supports the development of sustainable lightweight structures. Disposed bottle caps can be used to generate eco-friendly honeycomb cores, especially when combined with other eco-friendly components. A natural fibre-based laminate represents an alternative to synthetic fibres, matrices, and metals in skins for sandwich panels. This study evaluates the use of flax fibre laminates as sustainable skins for sandwich panels made from upcycled bottle caps core. Metallic skin cases are also tested as a reference. The influence of the amount of adhesive used to produce the panels is also investigated in a 22 full factorial design, together with an independent test carried out on samples made from natural fibres. The characterisation against flexural and low-velocity dynamic loads indicates that the flax fibre skin leads to specific core shear and flexural moduli up to 19% higher than in aluminium-based panels. Unidirectional flax fibres, however, reduce the energy absorption during impact. Flexural properties show that the most efficient design involves the least adhesive amount. Finite element models also show a good fit to the experimental results and indicate a 166% increase of energy absorption with the presence of multidirectional fibre laminates.