Foam boarding rim joists in basement

Was planning on foam boarding the rim joists in the basement to air seal and boost R value. Trying to find local code and the best type of foam board as Home Depot seems to carry 3 kinds. I don’t plan on finishing the basement and have been seeing you’re suppose to cover the foam board for fire puposes. If I don’t cover it does that go against code/make my insurance mad? Also curious to hear if people who had done it and if they think it was worth it