Foam is spray applied as a liquid and expands as a foam so it fills every single nook, cranny, crevice, hole, crack, and gap making a perfect air-tight seal every time, regardless of complex framing.
Foam has a "Real World" R-Value that is uncompromised by external forces like temperature and wind. Fiber Insulations such as Fiberglass (batt) and Cellulose merely slow down convection which accounts for 80% of heat loss. As the temperature drops, convection currents speed up and Fiber Insulations lose their effectiveness. Foam on the other hand stops convection. Wind is not a factor either for Foam due to its continuous air-tight seal.