1. SIPs have thermal ratings R-17.5 (4 inch) and R-26.4 (6 inch); conventional 2"x4" construction practices using batt and loose-fill materials typically have R-4. With less wood, panels reduce thermal bridging (the transfer of heat into or out of a structure through a solid piece of lumber). A 16-foot SIP wall section with one 3'x4' window contains 0% wood and 99% insulation. The same wall framed with 2"x4" on 16" centers has 20% wood and a variable amount of insulation.
2. If not installed properly, batt insulation is susceptible to voids. Batts are either jammed into narrow cavities, improperly split around wiring or around electrical boxes, or cut too short or too long. In some remodeling jobs, insulation is removed but not replaced. When used with a trussed roof system, batts won't cover up the bottom chords, allowing heat to transfer directly from the interior of the house into the attic area in the winter and from the attic into the house in the summer. A solid foam panel eliminates these problems.
3. Any air moving within a conventionally insulated wall or ceiling decreases the energy performance of batt insulation. When properly sealed, foam panels do not allow air movement.
4. Depending on proper installation and effective sealing of joints and openings, SIP construction lends itself to tighter-than-average construction. This is especially true when SIPs are used for both walls and ceiling because the systems are engineered to connect to each other easily and tightly.