A: The easiest way is to drill a small hole (about a ¼” diameter) through the drywall in an inconspicuous place like in the back of a closet. Then take a piece of wire with the end folded over to make a hook and push it through the hole and pull it back out. If you see strands of glass it is fiberglass, if you see pieces of what looks like shredded newspaper it is blown in cellulose and if you hit something that feels slightly soft but nothing comes out if it is spray foam.