What Materials Can Rats Not Chew Through?

Solid, cured concrete and stone are effectively impervious unless already cracked or poorly cured. Steel and galvanized hardware cloth resist gnawing — for rats specifically, use 19-gauge mesh with openings no larger than ½ inch. Heavy sheet metal (24-gauge or heavier) makes a durable barrier around pipes and wall penetrations. Steel wool is also effective, but only when packed tightly into a gap and held in place with caulk or expanding foam — the metal fibers injure a rat's mouth and the sealant keeps it from being pulled loose. These materials share two things: they're harder than the rat's teeth, and correctly installed, they leave no edge to start gnawing on.

Extension research lists wood, rubber, vinyl, plastic, aluminum sheeting, and even standard concrete block among materials rats readily gnaw through. Add drywall and gypsum board, lead sheeting, thin aluminum flashing, and expanding foam or caulk used alone — all common at NH home entry points like sill plates, utility penetrations, and trim. These fail for the same reason the hard materials succeed: they give a rat's teeth something softer to bite into, and foam or caulk on its own offers no resistance at all once a rat starts working at an edge.

Extension guidance stresses that rats "often gnaw into walls at corners or where joints provide an edge." A chew-proof material installed with a gap or a loose seam is only as good as its weakest edge. That's why professionals pack hardware cloth or steel wool into an opening and cap it, rather than relying on a single soft material to bridge a gap. Combining a hard barrier with proper sealing — not one or the other — is what actually holds.