Packing peanuts are not for insulation
Can I use plastic shipping peanuts for insulation in the walls of my 1879 balloon-framed house?
Roger S. Apted, Milton, WI
Roe A. Osborn, a former associate editor, replies: The very reason why plastic peanuts work well as packing makes them a bad choice for wall insulation. Plastic peanuts hold air that helps cushion whatever is being shipped. In a wall cavity, they would offer little resistance to air movement, so they would be of limited R-value.
Another problem is that newer, environmentally friendly cornstarch peanuts dissolve when wet. Moisture passing through the walls could make your insulation dissolve over time. In addition, a supplier told me that most plastic peanuts are not fire-resistant. My advice is to take your peanuts to a recycler and to insulate your walls with something more substantial.