Mice are the most common mammal species --- besides humans --- living in cities and their size makes it easy for them to squeeze through any tiny opening to live and breed in businesses and residences. Mice will often use insulation such as fibreglass as nesting material. If mice have set up residence in your home insulation you might hear them gnawing, scratching, squeaking and fighting in your walls and ceiling. Studies and experience have proved fibreglass is not a deterrent to mice.
Fibreglass is made of melted glass spun into fibres. Fibreglass insulation is the "sweetheart building material" for most builders, remodelers and homeowners, according to Tim Carter, Ask the Builder. Fiberglass itself in noncombustible, however the foil or kraft paper on fibreglass batt facings are combustible.
Mouse nests are about 4 to 6 inches in diameter and look like a ball of loosely woven shredded material. In "What Lies Beneath: Fiberglass Insulation," which appeared October 2009 in "Popular Mechanics," writer Tom Klenck states: "...mice like fibreglass. In fact, it's clear that fibreglass is one of their preferred construction materials. They move it from here to there, bunch it up and hollow it out. They nest in it, use it as a bathroom and, as far as I know, they may eat it, too." Consequently, mice using fibreglass for nesting material can quickly cause extensive damage to insulation in attics, ceilings and walls.
Mice and Insulation Studies
In a confined experiment, researchers at the University of Nebraska found that house mice caused significant damage to four types of fibreglass insulation: cellulose, fibreglass batt, fibreglass batt with fiberboard sheathing, and fibreglass batt with styrofoam sheathing. Expanding on that finding, researchers did a study on the impact of mice on five different types of insulation --- cellotex, fibreglass, rockwall, styrofoam and vermiculite --- in 1992. All the insulation materials were found susceptible to house mice damage. Researchers cited a 1982 German study that reported house mice destroyed all 12 types of insulation tested, including expanded polystyrenes, extruded polystyrenes, loose-fill perlite, mineral fibre, polyurethanes, pressed sawdust and spun glass.
"No insulation on the market is 100 per cent rodent-proof," according to Innovative Insulation, Inc., a retailer of insulation products. "Insulation materials alone will not completely deter rodent infestation." But manufacturers of cellulose insulation treated with boric acid claim it is "vermin resistant." The boric acid the cellulose is treated in is said to burn the eyes of mice, and female mice don't like to nest in it. Another relatively new insulation material, concrete foam insulation, is also claimed to be "fully rodent-proof," according to SaveGreenly.com.