Is this product "Expanded" or "Extruded" Polystyrene? Also, is this product rated for ground contact? (Intend to use under 6" garage slab)

All STYROFOAM(TM) brand insulation products are made of extruded polystyrene. This particular insulation board has a 15 psi compressive strength, which is typically used in applications that don't require much in the way of compressive strength, however we usually recommend a higher-than-average compressive strength for boards that will have significant loads, such as the weight of a vehicle, resting on top of them. Higher compressive strength prevents the foam from being crushed because it is sturdier. For a heavier load, such as a vehicles, we would typically recommend using a board from our STYROFOAM(TM) High Load series. Additionally, please note that a 4-6 mil polyethylene plastic waterproofing layer must be laid beneath the slab as well. For more information on calculating the load on your garage slab, visit the link below: http://dow-styrofoam.custhelp.com/app/answers/detail/a_id/3320/kw/safety For more information regarding our STYROFOAM(TM) High Load Products, please visit our product page at the link below: http://building.dow.com/en-us/products#!%7CUS%7C0%7C0%7C0%7C0%7C0%7C0 If you have any other questions about your project, please feel free to call us at 866-583-2583 and select prompt 8.