Spray Polyurethane Foam roofing, also known as SPF, is comprised of foam insulation that is protected by a silicone coating which is resistant to water and ultraviolet rays. This type of roofing system has excellent thermal resistance, is lightweight, and when installed properly, bonds well to the substrate. It is seamless and self-flashing, which makes the installation process very fast. Another advantage is that spray foam roofs are very inexpensive.
One of the downsides, however, is that the installation must be done exactly right (i.e. surface area prepared properly, right mix of chemicals, proper spraying, and the proper ambient temperature), otherwise the roof can fail catastrophically. Another problem is that hail can easily knock holes into the semi-soft foam. Birds are also attracted to some spray foam formulas and will peck chunks out of the foam to use for their nests. Once the silicone coating is gone, UV rays quickly eat up the foam and water can penetrate and travel all over the roof surface. This type of roofing system needs to be inspected annually to have additional silicone added to the areas that have weathered or been punctured.