The structure of a thin walled tube filled with light weight foam has wide engineering applications because of its excellent energy absorption capacity. When the structure is axially crushed, the interactive effect between the tube and foam core becomes a critical design consideration. Previous theoretical studies so far have largely been concerned with fully in‐filled tubes. In addition, the approach to quantitatively estimating the interactive effect is complex. To fill these gaps, a theoretical framework is established in this paper to predict the crushing behaviour of such structures with partial infill. Using the modified superfolding element model for shell and the volume reduction model for foam core, the mean crushing force is predicted through the energy method. As this formula relates the mean crushing force to the half plastic wavelength H, the interactive effect can be easily evaluated from the change of H.