The competing (but long dead) HD-DVD format had a combo-variant where you had a DVD layer and a HD-DVD layer on the same disc, like SACDs also have a backwards-compatible CD layer, but for Blu-rays something like that was never used, as far as I know.
Thus there are no commercial Blu-ray discs that can also be read by a plain DVD drive.
The only thing that comes kindof close are âMini-Blu-raysâ, i.e. the filesystem and data structure of a Blu-ray burned onto a regular DVD. These are mostly useful for homemade video, due to space constraints, and not all Blu-ray players support them.