3D visualization of ejecta-shell interaction in Cas A from model W15-IIb-sh-HD+dec-hr (see Table 1). The irregular isosurface describes ejecta with mass density >10^–23 g cm^–3; the colors represent the radial velocity in units of 1000 km s^–1 (the color coding is defined in the bottom right corner of the figure). The green volume rendering describes the mass density of the shocked shell material (color bar on the right of the figure). The upper right inset highlights the shell structure characterized by holes and rings, resulting from interaction with the ejecta.