I don't think any of them are solid. It wouldn't lend itself to casting and it would be an unnecessary cost for the manufacturer. My PuzzleProz DIYs have caps for the corners so they seem solid, but are hollow.
Old cubes made in the late 1970's are solid...
They are made by PolyThechnica, a old factory in Budapest, WAAAY before the Cube was introduced to the rest of the world.
Oh, the cubes are (obvioulsy) not being produced anymore