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Rodent exclusion materials

Quick answerVerified September 26, 2026

What is rodent exclusion materials?

Physical materials used to close the gaps rodents use to enter a building: metal wools and meshes, hardware cloth, sheet metal, concrete, and the sealants and door hardware around them. What decides whether a repair holds is gauge, mesh size and a hard, flat surface with no edge to bite. Foam, rubber, vinyl and plastic do not stop gnawing.

Reviewed by LTK editorial team

Where it fits

Holes sized to the animal. Rats can get through any opening wider than 1/2 inch, and mice through anything wider than 1/4 inch. A pencil or ball-point pen (3/16 to 3/8 inch across) is a quick gauge: if it fits, a mouse can get in. Measure the gap before you choose the material.
Hardware cloth that matches the target species. The published specification is woven 19-gauge, 1/2 x 1/2-inch mesh to exclude rats and 24-gauge, 1/4 x 1/4-inch mesh to exclude mice. Use woven or welded cloth. Cloth that is neither breaks easily, while woven or welded cloth keeps its shape when cut to fit around pipes. Holes 3 inches or more across should be backed with 1/4-inch cloth before patching.
Galvanized sheet metal and concrete where gnawing pressure is high. The same specification calls for 24-gauge or heavier galvanized sheet for wall and pipe barriers, 22-gauge or heavier for kick plates and door edging, and 14-gauge for perforated grills. Concrete should be at least 2 inches thick if reinforced and 3 3/4 inches if not. Rodent incisors curve slightly inward, so a flat, hard surface is difficult to start on.
Copper or stainless steel wool packed into small gaps. For openings under 3/4 inch that cannot be closed any other way, Nebraska Extension says to wedge copper or stainless steel wool tightly into the gap. For a long-term repair, work a quick-drying patching plaster into the copper wad before pushing it in, then smooth the outside over.
Doors, which are among the most common entry points. The gap between the door bottom and the threshold should not exceed 1/4 inch. On softwood doors, fit metal flashing or a metal channel to the lower edge, finished to within 1/8 inch of the edge at the sides and bottom.

Where it does not

This is the part the brochure leaves out, so it is the part worth reading.

Foam as the barrier. UC IPM lists insulating (expanding) foam among the materials that are ineffective for plugging mouse holes, alongside plastic screening, rubber, vinyl and wood. The federal wildlife damage handbook says spray-in-place foam and neoprene seals are not rodent-proof, and Nebraska Extension adds that sunlight degrades foam. CDC consumer guidance still suggests caulk or spray foam to hold steel wool in place. Treat foam as an air seal or a retainer, never as the thing stopping the rodent.
Plain steel wool as a permanent repair. Every source that recommends it calls it temporary. UC IPM says it may rust over time, the federal handbook warns of rust stains, and Nebraska Extension says coarse steel wool will eventually rust. On a job you are warrantying, specify copper or stainless and back the patch properly.
Rubber and vinyl door sweeps and weather stops on accounts with active rats. Rats and mice can quickly gnaw through rubber or vinyl weather stops, and the federal handbook photographs a large hole Norway rats chewed through a warehouse door weather strip. A sweep seals a gap. It does not stop gnawing unless it is protected by metal. A plastic door boot is only described as working where a door gets little use and its edges are hard for rodents to reach.
Lightweight metals and screen as rodent-proofing. Rats can gnaw through lead and aluminum sheeting, window screen, fiberglass, plastic and low-quality concrete or concrete block. Aluminum flashing and insect screen have their uses, but neither is a rat barrier unless it meets the gauges above. On vents, go no finer than you need: small mesh screens can clog with dust or freeze over, and 1/2 x 1/2-inch cloth is the published compromise between airflow and rodent control.
Metal-to-concrete details that are left to rust. Metal siding resting directly on concrete can rust and corrode faster, and siding should be installed with openings no wider than 1/8 inch. An exclusion job that corrodes open at the slab line in a few seasons has only delayed the callback.

Sources

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