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Blog · October 2026
What can mice and rats chew through?
Wires, plastic pipe, foam, drywall, even soft metal. Rodents gnaw because their teeth never stop growing, and given an edge to start on, they get through most building materials. Here is what holds and what does not.
- Teeth never stop growing
- Edges are the weak spot
- Foam does not hold
- Steel and concrete do
Want the materials list? Skip to what they chew and what stops them.
Start here
What can mice and rats chew through?
Mice and rats can chew through wood, plastic, vinyl, rubber, foam, caulk, drywall, wire insulation, aluminum sheeting, soft metals such as copper and lead, and concrete block. They have a hard time with steel, solid concrete and heavy hardware cloth. Their incisors grow continuously, about 5 inches a year in Norway rats, so gnawing never stops. University of Nebraska-Lincoln Extension says the teeth curve inward, which makes it hard for rodents to gnaw flat surfaces, round surfaces wider than 7/8 inch, or anything harder than iron, such as steel. Given a rough surface or an edge, though, they can quickly gnaw into most materials. That is why sealing uses metal and concrete, and why foam alone fails. Chewed wiring is a real hazard: UC IPM links rodent damage to electrical sparks and fires.
Why they gnaw
Teeth that never stop growing
Tooth facts from ICWDM and University of Nebraska-Lincoln Extension.
Rats and mice have paired incisors that grow continuously. ICWDM puts the growth at about 5 inches a year in Norway rats, and says gnawing on hard surfaces wears the teeth down. A rodent that stopped gnawing would have a problem, so they chew on everything, whether or not they are trying to get somewhere.
They do not chew at random, though. Nebraska Extension says rodents often gnaw into walls at corners or where joints in construction materials provide an edge. A flat face is hard to bite. A corner, a seam or a gap around a pipe is an invitation.
Chew or no chew
The chew list: material by material
If it is softer than steel and has an edge, assume a rat can get through it.
| Material | Can they chew it? | Source |
|---|---|---|
| Wood | Yes. Rats may gnaw a wooden door to widen a gap | UC IPM, Nebraska |
| Plastic, vinyl, rubber | Yes | Nebraska G1530, UC IPM |
| Expanding foam and caulk | Yes. Foam alone will not stop entry | UC IPM, ICWDM |
| Wire insulation | Yes, in homes, vehicles and equipment | UC IPM, MSU Extension |
| Aluminum sheeting | Yes, thin sheeting | Nebraska G1530 |
| Copper and lead | Yes, rats gnaw soft metals | UC IPM |
| Concrete block | Yes | Nebraska G1530 |
| Steel wool | Holds for a while, but plain steel wool rusts | Nebraska G1530 |
| Galvanized steel, solid concrete | Hard for them; used for sealing | Nebraska G1530, MSU Extension |
Chicken wire is a weak spot people miss. UC IPM says never use lightweight chicken wire, because rats can pass right through the openings. Plastic bins are another: ICWDM says galvanized steel containers in good condition resist rats better than vinyl or plastic.
Wires and fire risk
Chewed wiring: why it matters
Wiring hazards from MSU Extension and UC IPM.
Any kind of wire
MSU Extension says rodents will gnaw wiring of any kind, in vehicles, equipment or buildings, causing shorts and electrical hazards.
Sparks and fires
UC IPM says roof rats in attics can cause considerable damage and safety concerns, including electrical sparks and fires.
Gas lines too
UC IPM says rats may chew directly on natural gas lines, creating explosion and fire hazards.
Where to look
Attic runs, wires in the crawl space and cables behind the stove and fridge. Look for bare copper and shavings.
Rodents in the engine bay are a separate problem; our car wiring guide covers it. If you find bare wire in the house, call an electrician before you touch it.
Pipes, foam and walls
Can they chew through the ceiling, water lines or foam?
The answer to most of the I-wonder-if-they-can questions is yes.
Ceilings and drywall
Yes. Gnaw marks on wall materials are a standard rodent sign, per ICWDM. A rodent in the attic or wall can chew into a room, usually at a corner or edge.
Plastic water lines
Plastic is on every extension list of chewable materials, so plastic supply lines are not immune. Check under sinks and in the crawl space for gnawing.
Spray foam
UC IPM lists foam among materials rats chew through. ICWDM says expanding foam reduces heat loss but will not prevent rodent entry.
Insulation
ICWDM says mice are very destructive to rigid foam, fiberglass batting and other insulation in walls and attics.
Food packaging
Cardboard, paper and thin plastic bags are no barrier. Use glass, metal or thick, hard plastic with lids.
Wooden doors
A rat may gnaw a wooden door edge to widen the gap under it, according to UC IPM. Metal edging stops that.
Repairs for chewed water lines, ducts and wiring are covered on our cost page. For what to keep and what to toss, see what to throw away after mice.
Seeing gnaw marks?
Find the gnawing before it finds a wire
Call or send the form. We find where the rodents are getting in, seal the gaps with metal and trap what is inside. The price is in writing before any work starts.
What holds them
The materials rodents cannot chew through, with specs
Metal and masonry, at the right gauge and thickness.
| Material | Spec from Nebraska Extension G1530 | Typical use |
|---|---|---|
| Hardware cloth, rats | 19 gauge, 1/2 by 1/2 inch mesh | Vents, crawl space openings |
| Hardware cloth, mice | 24 gauge, 1/4 by 1/4 inch mesh | Smaller openings, vent screens |
| Galvanized sheet metal | 24 gauge or heavier | Gaps, door and wall edges |
| Perforated sheet metal grills | 14 gauge | Vent covers |
| Aluminum | 22 gauge for frames and flashing; 20 for kick plates; 18 for guards | Doors, flashing |
| Concrete | 2 inches reinforced; 3 3/4 inches not reinforced | Foundation gaps, slab edges |
| Brick | 3 3/4 inches thick, joints filled with mortar | Walls and foundations |
MSU Extension recommends sealing with mortar, concrete, sheet metal or hardware cloth of 19 gauge or heavier with no openings over 1/4 inch. For a small gap, Nebraska suggests copper or stainless steel wool wedged tight, since plain steel wool rusts. How to put these together on a house is on our exclusion and sealing page.
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Straight answers
Chewing questions
What can mice and rats chew through?
Wood, plastic, vinyl, rubber, foam, caulk, drywall, wire insulation, cardboard, thin aluminum, soft metals such as copper and lead, and concrete block. Steel, solid concrete and heavy hardware cloth are the materials that hold them.
Can mice chew through the ceiling?
Yes. Drywall and ceiling materials are soft, and ICWDM lists gnaw marks on wall materials as a sign of rodents. They usually start at a corner, seam or edge.
Can rats chew through concrete?
Nebraska Extension lists concrete block among materials rodents gnaw. Solid concrete at least 2 inches thick when reinforced, or 3 3/4 inches when not, is what the same guide recommends for rodent-proofing.
Will steel wool stop mice?
For a while. Nebraska Extension says coarse steel wool works as a temporary plug but will eventually rust, and suggests copper or stainless steel wool wedged tight, with permanent repairs in metal or concrete.
Why do mice chew on wires?
Their incisors grow continuously and gnawing wears them down, according to ICWDM. Wire insulation is soft enough to chew, so wires in their path get gnawed.
Can rats chew through PEX or plastic water lines?
Extension guides list plastic as a material rats and mice can gnaw, so plastic lines are at risk where rodents are active. Check under sinks and in the crawl space for gnaw marks and leaks.
Is chewed wiring really a fire risk?
It can be. UC IPM says rodents in attics can cause electrical sparks and fires, and MSU Extension says gnawed wiring causes shorts and electrical hazards. If you find bare or damaged wire, have an electrician look at it.
Keep reading
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Sources
Last reviewed October 2026 by the Rodent Control Oxford team. Biology and control standards follow Mississippi State University Extension and the CDC. Price ranges are labeled benchmarks; your price comes in writing after we inspect.
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