Density change during the manufacturing process of PU–PE open cell auxetic foams

This paper describes a modified manufacturing route involving a large change in density in auxetic negative Poisson’s ratio (NPR) foams. Density change of auxetic foams after manufacturing is a common feature for this porous material. Samples of open cell PU–PE (i.e. the combination of polyurethane–polyethylene) foams with NPR are produced from two similar native materials using both the classical and the novel custom manufacturing methods. In the classical manufacturing route the cooling process is typically carried out with the foam in a confined state. Conversely, in the new manufacturing process it was substituted with a release process. Samples were subjected to both tensile and compressive loading, as well as density measurements. A thorough mechanical characterisation of the foams is described, linking the mechanical properties with their change in density after conversion into auxetic.