drain and vent insulation
 

After removing the kitchen sink and the wall, I notice the builders packed some plaster around the drain and vent pipes where they pass through the framing.
I assume that this is method of fire blocking. So, as I have knocked away a lot of it, would some type of spray foam be advised to fill in the spaces? Thanks

They make fire rated caulking just for this purpose. Unless the spray foam is fire rated then it would not meet code.