Spray foam insulation is ideal for crawl spaces due to its water-repellent properties and resistance to biological growth.
For stapling insulation, 20-gauge staples are recommended, though 19-gauge and 23-gauge staples can also be used.
Use R-19 or R-21 kraft-faced fiberglass insulation for 2x6 walls to ensure it fits snugly without being too loose or too tightly packed.