Unless something new is out there now, insulating foam is very flammable. A custom applicator I know lost his business when a large shop he was spraying caught fire and burned. The engine on his applicator rig back fired and started the fire. He lost the rig, his new pick-up, and the cost of replacing the building. Apparently he was under-insured.
The foam is self extinguishing, but only when encapsulated. Example, covered in sheet rock. Uncovered, any flame which starts at the bottom quickly walks up the wall and across the roof. It produces a thick and noxious smoke.
There is no better insulator on the market. And the foam, if properly applied will completely eliminate airflow through the walls. I have seen it applied along the wall studs and lightly on the inside surface of a home's wall sheeting. It makes for an incredibly strong and almost sound proof exterior wall in a home.
Evidently, this stuff is "closed cell" and supposed to be flame retardant.
