Expanded Ploystyrene (EPS)
EPS is a molded closed-cell expanded polystyrene foam plastic in the form of flat panels or differing shapes. R-values vary depending upon the thickness of the board and the denisty of the product. EPS is used as a general, nonstructural, thermal insulation material for walls, roofs, panels, door cavities, perimeters of foundations and basements. EPS can also be  tapered to provide proper drainage on a roof top application.

Extruded Polystyrene (XPS)
XPS, extruded polystyrene insulation has superior long-term thermal properties, has a high resistance to water absorption, is available in high comprssive strengths and is easily handled and installed. XPS comes in various thicknesses, widths and lengths, in either flat panels or tapered panels. XPS can be used in both roof and wall applications.