How to Know What Insulation is Behind Your Walls

What it is: Finely spun glass fibers create a lofted material that can be rolled as batting; it can also be sprayed into walls as loose fill. It remains one of the most popular types of insulation.

How it works: Fiberglass works as a barrier by trapping air inside pockets of fluff; that's why it loses its effectiveness when compressed by the weight of boxes or other heavy items.