Copying a plastic skull with spray foam

So I saw a video online by Dr. Kreepy where he made copies of a plastic skull using spray foam.  I thought I would give it a try.

Here is my spray foam and my skull.

I cut my skull in two using a heavy duty Xacto knife. I cut a square in the backside to spray the foam into.  I rubbed the inside with petroleum jelly so that the foam would not stick to it.

I taped the skull back up with duct tape.

I sprayed the foam inside.  Over time, some of the foam would expand outside of the hole in the back and I would cut off this excess. At the end of day one, everything looked good and extra foam was not coming out.

 I walked away for three days and came back to this. Ack! My foam expanded and blew out the tape on the mold.

 

He's a bit misshapen.

 But from the front he doesn't look too bad.

I will definitely try this again, but use way less foam (I had filled it up about 90%) and add more duct tape to prevent it from blowing out the mold again.  I also left it to dry in the hot garage thinking this would speed up the drying time, but I think I will bring him in the house to dry the next time around.