Geocell reinforcement of soil has been used successfully for many years in a wide variety of applications, some of which have tested the boundaries of current understanding of the functioning of the geocell–soil composite systems. This paper discusses the results of uniaxial compressive tests performed on geocell packs of different sizes. The packs were instrumented and the deformation within the packs studied. The boundary conditions imposed on the geocell pack in a laboratory test governs the deformation throughout the pack and has to be taken into account when interpreting the test results. This study shows that the strength of the geocell composite structure is indirectly proportional to the size of the individual cells and that the strength reduces with an increase in the number of cells in the structure.