Spray foam insulation is made from polyurethane, which expands and hardens to form an insulating barrier.
The thickness of R38 batt insulation is usually about 12 inches. This substantial thickness helps to provide excellent thermal resistance, making it a popular choice for insulating attics and other areas where maintaining a high level of energy efficiency is crucial.
Insulation should face the living space, with the vapor barrier (the paper or foil backing) towards the interior to help control moisture.