Answer to Question 1
An open cell process is done rapidly causing the material to actually burst and create large pockets of air within the material. For a closed cell, the beads would not fully expand to bursting, but the air is still enclosed within the bead. Three examples of open cell foam include: sponges, nerf footballs, and some door mats. Three examples of closed cell foam include: shoe soles, styrofoam cups, and insulation for drinking mugs.
Answer to Question 2
The part design restraints are less detailed. It is a non-pressure process requiring less expensive machines. Because of these lesser restraints the molds can be formed out of any material: plaster, wood, clay, metal, silicone.