Concentric steel spherical shells (or semiespherical)
at least two sheels, sparated by an arrangement (icosahedron, for example) of rubber pads.
It works in similar way that a rubber springs composed by a metalic plain washer joined with a rubber washer, then joined with a metalic washer and then again rubber washer....This arrangement in order to get more linear-like curve force-versus-deformation
I hope this can help you
Sincerely
Shieldmaker