Steel wool for mice is one of the most popular home fixes in the country, and for good reason. It is cheap, easy to find, and the CDC names it first when it explains how to plug small holes. But a wad of steel wool pushed into a gap is not the same thing as a sealed gap. Installed halfway, it rusts, loosens, or gets worked out, and mice find their way back in.
This guide covers what steel wool can and cannot do, how to install it so it stays put, where you need sturdier materials like hardware cloth or metal sheeting, and how to check that your sealing job is holding.
The Short Answer: Does Steel Wool Keep Mice Out?
Yes, as part of a proper seal on small holes. The CDC recommends filling small holes with steel wool and putting caulk around it to keep it in place, or using spray foam to hold it. The University of California Statewide IPM Program describes steel wool scouring pads as good temporary plugs that may rust over time.
So steel wool is a solid first layer for small gaps, but not the right material for large openings, and not a one-time job in damp spots. It also does nothing about mice already living inside. If you find fresh droppings in several rooms, you will also need traps or a licensed pest control professional.
Why Sealing Matters More Than Anything Else
According to the CDC, mice can fit through a hole the width of a pencil, about 1/4 inch. UC IPM adds that house mice can squeeze under gaps 1/4 inch tall and through openings 3/8 inch wide, and it calls exclusion the most successful form of house mouse control. Its advice is simple: close all gaps and openings larger than 1/4 inch.
Oregon State University's Solve Pest Problems site notes that mice tend to use existing holes and are not very effective at gnawing new ones. That is good news: every gap you close is one less ready-made doorway.
How to Use Steel Wool for Mice: Step by Step
Step 1: Find the Gaps
Walk the outside of your home with a flashlight. The CDC lists the roof line, doors and windows without weather stripping, the gap between the foundation and the ground, attic and crawl space vents, and every hole where utility lines enter. Inside, check under cabinets, behind appliances, around pipes under sinks, and around dryer vents. For a full map, see our guide on how mice get into your house.
Step 2: Decide If Steel Wool Is the Right Material
Oregon State's guidance is a useful rule of thumb: fill entry points as small as a dime with sealant and steel or copper wool. Anything bigger, such as a hole in a foundation or a wide gap around a vent, calls for metal, hardware cloth, or concrete. Steel wool alone is a plug, not a patch.
Step 3: Pack It Tight
Wear work gloves, since steel wool sheds sharp fibers. Tear off enough to overfill the hole, then push it in firmly with a screwdriver until it fills the whole opening. A loose plug is easy to work out of the hole.
Step 4: Lock It In With Caulk or Foam
Run a bead of caulk around the steel wool, or use spray foam, as the CDC recommends. The caulk or foam is the holder, not the barrier: UC IPM warns that rubber, vinyl, expanding foam, wood, and other gnawable materials are ineffective for plugging mouse holes on their own.
Step 5: Check It Every Season
Steel rusts, especially in damp crawl spaces and along foundations. Look at your plugs in fall and spring, and replace any that are crumbling. For wet spots, consider copper wool (see the FAQ below).
Where Steel Wool Is Not Enough
Some openings need stronger or more breathable materials:
- Larger holes: the CDC recommends lath screen or lath metal, cement, hardware cloth, or metal sheeting, cut to fit around pipes.
- Vents: do not stuff vents with steel wool. Oregon State recommends welded wire hardware cloth with 1/4-inch openings to exclude mice, which keeps air moving.
- Foundation cracks and utility openings: UC IPM says to seal these with metal or concrete.
- Doors: install door sweeps and weather stripping, as the National Pesticide Information Center advises.
- The rest of the property: the CDC also says to fix gaps in trailer skirting, use flashing around the base of the house, and seal outbuildings and garages. If your garage connects to the house, our guide on how to keep mice out of the garage covers it in detail.
- Electrical boxes and live wiring: steel wool is metal. Keep it away from outlets and exposed wires, and ask an electrician to seal gaps around electrical boxes.
If You Find Droppings While Sealing
Do not sweep or vacuum them. The CDC says to air the space out for 30 minutes, wear rubber or plastic gloves, soak droppings and nests with a bleach solution (1.5 cups of bleach in 1 gallon of water) or an EPA-registered household disinfectant for 5 minutes, then wipe up with paper towels.
Cheat Sheet
- Mice fit through a 1/4-inch hole, about the width of a pencil (CDC).
- Steel wool is for small holes, roughly dime-sized or smaller.
- Pack it tight, then hold it in with caulk or spray foam.
- Foam, caulk, rubber, and wood alone are not mouse barriers (UC IPM).
- Larger holes need hardware cloth, metal sheeting, lath, or cement.
- Cover vents with 1/4-inch hardware cloth instead of stuffing them.
- Check plugs each fall and spring, and replace rusted ones.
- Sealing keeps mice out. It does not remove mice already inside.
Where BioGuard Fits
We sell BioGuard Natural Rodent Repellent, a pack of 12 scent balls infused with peppermint and cinnamon essential oils. It is not a substitute for steel wool, caulk, or hardware cloth. Where it can help is as an extra layer after you seal: near sealed entry points in a garage, shed, or storage area, along garden edges, or in a car engine compartment. Replace it every 4 to 6 weeks, sooner after heavy rain outdoors, and keep it away from children, pets, and food. It is a repellent, not a removal product, and results vary.
Frequently Asked Questions
Can mice chew through steel wool?
Neither the CDC nor UC IPM addresses this directly. Both treat steel wool as a plug material, and UC IPM calls it temporary. In practice, the weak spot is a loose plug that can be worked out of the hole, or one that has rusted apart. Pack it tight, hold it in with caulk, and check it each season.
Is copper mesh better than steel wool?
Oregon State lists steel or copper wool for small gaps and around pipes and cables. Copper does not rust the way steel does, which makes it a sensible choice for damp areas such as crawl spaces and outdoor pipe openings.
Can I use expanding foam instead of steel wool?
Not by itself. UC IPM lists expanding foam among the gnawable materials that are ineffective for plugging mouse holes. Use foam or caulk to hold steel wool or copper mesh in place.
Will steel wool get rid of mice already in my house?
No. Sealing stops new mice from getting in. For mice already inside, the CDC recommends snap traps placed where you see activity, and a licensed pest control professional is the right call for a larger problem. Our step-by-step guide on how to get rid of mice in the house walks through the full plan.
Sources
- CDC, How to Seal Up to Prevent Rodents
- CDC, How to Clean Up After Rodents
- CDC, How to Trap Rodents
- University of California Statewide IPM Program, Pest Notes: House Mouse, Publication 7483 (revised July 2025)
- Oregon State University, Solve Pest Problems: Mice
- National Pesticide Information Center (Oregon State University), Mice