Volum3 from Romania made a tutorial on how to make large molds with several 3D printed parts acrylic plaster and silicone that can be used to cast relatively big objects from polyurethane foam.
Instructables page:
http://www.instructables.com/id/How-to-Make-a-Cheap-Silicone-Mold-of-a-3D-Printed-/
Instructables page:
http://www.instructables.com/id/How-to-Make-a-Cheap-Silicone-Mold-of-a-3D-Printed-/