Mice and other rodents seek refuge when it begins to get cold outside. They will move into a house if they can find a way in. Rodents create a variety of problems. They eat or destroy food meant for humans and pets, gnaw anything they can get to and leave droppings wherever they go. They also multiply quickly. It is best to prevent the rodents from getting into the house at all, and expanding foam is an inexpensive solution to a potentially big problem.
Select the type of foam you need. Polyurethane and latex are the two types of foam sealants available. Polyurethane expanding foam is porous when dry, and it is possible to cut it into an appropriate shape with a bread knife. Latex foam dries into a rigid shape that is difficult to manipulate. It can be sculpted only while it is wet.
Search for holes around the house, such as in the siding close to the foundation and around cables and pipes that lead into the house. Do not overlook small holes. Some rodents, such as house mice, can squeeze through holes that are as small as 6 mm (1/4 inch) across. Also check for openings in areas where you have found some evidence of rodents, such as gnawed items and rodent droppings.
Wear protective clothing to prevent the foam from dripping onto your skin. It is difficult to remove expanding foam from skin and clothing.
Pack steel wool into the opening until it is tightly sealed. This will provide a base for the expanding foam that rodents cannot chew through. Spray the foam onto the steel wool and use a putty knife to shape it as desired. Work quickly because the foam dries fast.