I’ve stated many times the we use 30 lb Precision Board exclusively in our shop. This is true when it pertains to CNC routing… but when we are hand sculpting high density urethane that will be coated with sculpting epoxy we sometimes use four pound foam. It is so soft I can practically carve it with my hands.
The rough armature for the robot body was a great place to use this less dense foam. It needed to be fit around the welded steel armature and then roughed into shape. I used there layers of 3″ four pound foam. Since I was going to coat it in sculpting epoxy I wasn’t concerned with gaps or rough edges. I used PB Bond fat set which cures in only one hour. I glued it up before I went to lunch and when I returned I was able to remove the clamps and get busy sculpting over the new form.