I'm looking for a soft foam (sprayed or mat) roofing material for a flat roof in order to discourage seagulls from dropping everything they can on the roof. Somebody must have dealt with this problem before, but I can't find any suitable material that doesn't cost a fortune.

Not sure about a foam board but Smith and Wesson makes a good product. Wish I could help better. Have you heard about runnning a line of monofilament fishing line back and forth just above the roofing, it trips them and they can't figure it out so they go to your neighbors house.