The keyword here is "focus": a spherical surface like this does not focus sun rays, you need a parabolic surface for that. While it would be possible to shape a

The keyword here is "focus": a spherical surface like this does not focus sun rays, you need a parabolic surface for that. While it would be possible to shape a film or another foldable material into a parabolic profile playing with air pressure and a specially crafted frame, I wonder what would be the advantage over a rigid parabolic mirror. The foldable/inflatable part is only an advantage for aerospace applications where size and weight are at premium.