Which insulation is not gnawed by mice? - briefly
Mice cannot gnaw metal‑based or concrete insulation, such as steel wool, metal sheeting, or rigid foam with foil facing. These hard, non‑organic materials offer no nutritional value, so rodents avoid them.
Which insulation is not gnawed by mice? - in detail
Mice damage most soft or fibrous insulations because their incisors can easily cut through cellulose fibers and flexible foams. Materials that remain intact under rodent pressure share three characteristics: high tensile strength, abrasive surface texture, and chemical composition that is unpalatable or toxic to rodents.
- Mineral wool (rock or slag wool) – dense glass fibers bound with strong resin create a hard, abrasive matrix that rodents cannot easily bite through. The resin also contains compounds that deter gnawing.
- Closed‑cell spray foam – expands into a rigid, cellular structure that hardens to a density of 2 lb/ft³ or greater. The cured foam resists penetration and lacks the softness that attracts chewing.
- Rigid foam board (extruded polystyrene, XPS) – solid panels with a smooth, dense surface provide a physical barrier. While some rodents may attempt to chew, the material’s hardness significantly reduces successful damage.
- Polyisocyanurate (polyiso) board – similar to XPS but with higher compressive strength, offering additional resistance to gnawing.
- Metallic sheathing or foil‑faced insulation – metal layers act as an impenetrable shield; rodents cannot bite through metal.
Materials that are ineffective against rodents include fiberglass batts, cellulose blown‑in insulation, and open‑cell spray foam. Their loose fibers and softer matrices are easily shredded.
Installation practices that enhance rodent resistance:
- Seal all entry points (gaps, cracks, utility penetrations) with steel wool, copper mesh, or cement‑based caulk before installing insulation.
- Apply a thin layer of rodent‑deterrent spray or bittering agent to the exterior of foam boards where exposure is possible.
- Use a continuous barrier of rigid foam or mineral wool around the building envelope, especially in crawl spaces and attics where mice commonly travel.
- Install metal flashing or mesh over insulation seams to prevent rodents from accessing the material from behind.
By selecting high‑density, hard‑surface insulations and combining them with comprehensive sealing, the risk of rodent chewing is minimized, preserving thermal performance and structural integrity.