What @jiivita means by semi transparent is having an alpha value other than 1 or 0. The game only supports binary alpha (is that right idk), in other words only opaque or fully transparent with nothing in between. Trust me I have tried.
You can still make them semi transparent on the surface. And you can also integrate them as a mesh. Legit all you have to do is put a grey pixel grid. But the interior would still be transparent because it doesn’t exist.