Vermiculite insulation is a pebble-like, pour-in product that is light-brown, gray, or gold, often with shiny flakes or small accordion-like pieces.
Use serrated blades or putty knives to gently remove foam insulation, and for tougher areas, use a power drill or grinder.
Use R-13 or R-15 kraft-faced fiberglass or mineral wool insulation for 2x4 walls to ensure proper insulation.