The purpose of buildings for people is to isolate them comfortably from a hostile exterior climate. The purpose of insulation is to develop this climate isolation beyond minimum shelter to allow complete modern interior climate control. To achieve this climate isolation in your Denmark, Fryeburg, or Portland, ME home successfully requires full isolation between interior and exterior temperatures, air and moisture. The two climates must not mix in the insulated building cavity. The system must also be reversible so the building may be both heated and cooled efficiently.
Spray foam achieves the climate isolation necessary by its very nature as a solid cellular plastic - fully adhered in the thin space of the building cavity. Exterior and interior climates cannot mix so no compromise of climate isolation can occur due to the exterior climatic conditions, however severe.
Study the Six Mechanisms of heat loss or gain in order to fully appreciate the forces acting on a wall and how spray foam Climate Isolation solves energy and building problems.