Although SIPs are available with either a Polyurethane (PUR) foam core or Expaned Polystyrene (EPS) core, PUR foam is a far better insulator and offers the best physical properties of any available insulating foam.

HIGHER R-VALUE: Polyurethane has a stable R-value of R-7 per inch of thickness, versus R-4 for EPS, you can achieve R-25 with 4.5" walls, whereas EPS-insulated walls would have to be nearly twice as thick to attain the same R-value.  

HIGHER FIRE RATING:  Safe and easy to use, PUR foam has better fire, flame and smoke characteristics and will not melt. It can withstand constant service temperatures up to 1200°F and will only char up to 1050°F, unlike EPS, when tested has melted at 260°F (this number can fluctuate from one EPS manufacture to another)

BETTER ADHESION:  All panels are "framed and foamed" in the factory.  If you think of the characteristices of the foam you can purchase in a can and spray for insulating electrical boxes, etc.  Note how the foam expands into all the voids and adheres the exposed surfaces.  This is similar to the properties of polyurethane, the foam chemically bonds to all voids, in this case the interior of the panel.

BETTER WIND LOAD:  Greenix Panels range between five and seven times stronger than traditional framing. Furthermore, structures built with Grenix Panels are highly resistant to wind damage and can be designed for areas with stringent wind or seismic lateral (shear) bracing requirements.