The recent advances in the additive manufacturing (AM) have enhanced the development of light-weight, energy-absorbing structures in many aspects with precise, designed configurations of the internal structure. Given the range of potential materials many possible variations exist compared to the existing polymer-based foams. The advantages of rapid prototyping, enabled through AM, allows a streamlined process in obtaining a structure of desired mechanical behaviour. In this work, development, and design variation of a flexible lattice structure with core strut modification is demonstrated. The core struts are varied in terms of shape and density and are fabricated using vat photopolymerisation with Formlabs Flexible 80A resin and experimental methodology is outlined for the characterisation of the printed specimen under compressive loading. Mechanical characterisation under three different compression rates presents that the implementation of the core strut increases the elastic modulus of the lattice structure. The enhanced stiffness effects are further increased with the variations in shape, while the evaluation of the density variations shows significantly different deformation behaviour and strain rate sensitivity. The behaviour of each specimen types is discussed further in terms of their functional viability and potential applications where the design specific behaviour and small, lightweight form factor can be most effectively utilised.