The NPS Rodent Exclusion Manual (http://www.twpinc.com/pdf/RODENT-EXCLUSION-MANUAL.pdf) says, hardware cloth is the best, and one of the easiest, materials to use for screening foundation vents, open pipes, and other holes. It effectively excludes mice and most native rats. However, light-gauge hardware cloth is not entirely resistant to more aggressive animals, such as Old World rats.
Use 16- to 19-gauge, welded-at-each-joint, ½-inch by ½-inch-mesh, galvanized-after-welding wire screen to exclude larger animals or aggressive rats. This is extremely strong material, and will last 10 to 20 years due to its heavy zinc coating.
Use 19- or heavier gauge, galvanized, ¼-inch or smaller mesh hardware cloth to keep smaller animals (e.g., mice) out. Covering hardware cloth with metal window screening also keeps insects out.
Stainless-steel Hardware Cloth. Cover floor drains with ¼-inch-mesh, heavy 16- to 19-gauge stainless-steel hardware cloth, and be careful to not leave any openings around the sides any larger than ¼ inch. Covering drains will increase clogging, so be sure to inform building maintenance staff when you install these screens.
Metal Window Screening. Metal window screening is not an adequate protective material for rodent-proofing, and it should only be used on windows to keep insects out. Plastic window screening does not provide any rodent-proofing qualities at all. This site and its content such as text, graphics, images, illustrations, video clips, and other material are for informational purposes only. The content is not intended to be a substitute for professional advice. The user should not rely on any information on these pages to replace consultations with qualified professionals to meet the user’s individual needs.