The behaviour of orthogonal layers of aluminium and mild steel tubes under lateral compression is considered. The results for each material are presented separately in Parts I and II of the paper. In all the tests the initial separation of tubes in the same layer is sufficiently large to preclude contact being established between adjacent tubes as they deform. Part I: Aluminium systems are examined and two principal categories of behaviour are identified. As well as providing basic load-deflection data in a suitably non-dimensionalised form, certain particular features of the modes of deformation of individual tubes in the systems are examined in detail. Part II: This presents data and observations concerning mild steel systems. Of especial interest is the difference between the behaviour of as-received tubes, which develop cracks in the regions of greatest deformation, and that of annealed mild steel tubes which show similar characteristics to those of the aluminium systems.