The box had to be big enough to leave about an inch of wall thickness around my whole part. This was to ensure that the mold held its shape throughout the process. However, I had some issues creating my silicone mold. I had to create some method of holding the ball up in the air, since I had features pretty much all around my part. I decided on making a riser out of clay and a funnel, which would also act as my pour spout. I also thought it might help with having extra resin to fill in any gaps as the plastic was poured.