This is a 3d printable mould for a bath bomb, it comes in four parts due to the opposing angles of the icosahedron. You'll probably have to split the model in your slicer. The top and bottom are the same, each side is the same. I split the top/bottom print in half and glued later to prevent lifting of corners off the print bed.
This is version one, if you are going to revise this I would recommend adding some pins on the two side pieces so they index with each other and potentially make a sleeve to slide over the two side pieces and bottom piece to lock together.
I taped the two sides and bottom together, then packed in the bath bomb mixture. Levelled the top flat, then packed in the top mould with a slight hump so as it would be a tight pressure fit when joining the two pieces together. There is probably a better way but the picture on the left was my first attempt so it can't be that bad. (If this doesn't make any sense just re-read when you are trying to use the mould and it will make a great deal more sense).
This should make around a 200gram bath bomb after the moisture leaves the product.
**I have uploaded two files; one will look like a box until it is split in your slicer. If this is not possible there is another file which is one side piece and one top/bottom piece (Print this twice for a full mould)