Benefits of polyurethane spray foam insulation:

Moisture Barrier

Closed cell polyurethane spray foam insulation Acts as great moisture barrier.

Closed cell polyurethane spray foam insulation do not absorb water its water perm is less than 1 at 2 inches thick. thus it inhibits Mold and mildew.

Closed cell polyurethane spray foam insulation can be used in higher density as roofing materials. ( it has to have the proper UV protective coating )