Pictured you’ll see my screw driver stabbed into closed cell spray foam applied to the underside of the floor sheathing in a crawl space in New Orleans. I always check to see if the foam was sprayed on correctly. There should be at least 1.5 inches of closed cell to have a proper thermal break so not a lot is needed or advised. I think it’s best practice to shoot for about 2 inches or to go a little over. I commonly find 1 inch of closed cell and write it up as improperly applied foam. Many home inspectors are against spray foam for various reasons. I’m not trilled with it either but in my opinion, no other type of insulation should be in a crawl space in South LA.