Lightweight, energy-absorbing structures are needed in many areas where the protection and
threat mitigation of fragile personnel and objects are essential. Hence, the investigation of development
and characterisation of energy-absorbing materials are crucial. The recent advances
in the additive manufacturing (AM) have enhanced the development of such structures in many
aspects with precisely designed configurations of the internal structures. Given the range of
potential materials, many possible variations exist compared to the traditional polymer-based
foams. The advantages of rapid prototyping, enabled through AM, allows a streamlined design
process in obtaining a structure of mechanical behaviour suitable for intended applications. In
this work, the development and fabrication of a flexible polymer-based lattice structure with
core strut variations are demonstrated. A re-entrant honeycomb unit cell based lattice structure
is chosen in a sandwich configuration with the implementation and modification of core struts
for further investigation. The designed lattices are fabricated using stereolithography (SLA), a
type of vat photopolymerisation, utilising the Formlabs Flexible 80A® resin. The core struts
are modified in terms of shape, density and number of inclusions within the internal structure of
the lattice. The mechanical characterisation of the samples under uniaxial compression is carried
out at the strain rates of 0.005, 0.9 and 108 s-1 and the appropriate experimental apparatus
and the diagnostics are developed and used for this purpose. The stress-strain responses reveal
that the variations in the core struts affect the overall deformation behaviour of the structure,
as well as the strain rate dependence of the relevant mechanical parameters. Anisotropic nature
of the lattices are also investigated by uni-axial compression of the lattices positioned at 45◦ and
90◦ angles. The theoretically obtained parameters, from the formulations only dependent on
the relative density, and the parameters calculated from the measured values are evaluated and
compared, providing the insight that the the structural geometries influence the characteristic
behaviour of the lattices over relative density or the material, highlighting the significance of
the chosen structural design of the lattices. Finally, the discussion of the research findings in
terms of the recommended applications of the each sample type, the functional flexibility and
adaptability are presented.