Expanding foam is a product which is designed to expand and harden upon contact with the air. It classically comes in canisters with spray nozzles, making it easy to apply the foam in a wide variety of situations. There are a number of uses for expanding foam, with most hardware suppliers stocking several types which can be utilized in many different applications. Most companies clearly list suggested and recommended uses on their products on the packaging, although some consumers may think outside the box when it comes to ways to use expanding foam.

Classically, expanding foam is stored under high pressure. When a user activates the spray nozzle, the pressurized contents spurt out, and they start to expand. As the contents expand, they develop a foamy appearance and they start to harden. Expanding foam can grow exponentially in size, which means that people need to be careful when they use it so that they do not apply too much. Latex, polyurethane, and a variety of other materials can serve as a base for expanding foam, and waterproof, fire resistant, and other specialty versions are available.

In construction, expanding foam can be used as insulation, since foam has some excellent insulating qualities. It may also be used to seal holes, with expanding home sealant also being useful for minor repairs. Expanding foam can be used around door and window frames to create a tight seal, and it can also be used to plug holes used by insects and animals. Expanding foam can also be used as an adhesive, with several companies making foam adhesive.

People also utilize expanding foam to make casts of various objects. A small amount of expanding foam can be inserted into a cast and allowed to expand, creating a replica of an object. Prop masters in film and television often use expanding foam for this purpose to create lightweight, inexpensive props which can be finished to look like more solid objects. The tendency to conform around a mold or object also makes expanding foam useful for customized product packaging, with shippers making expanding foam packaging to protect delicate items in transit.

A specialized type of expanding foam is used in fire suppression, especially with chemical fires. The foam is designed to quickly fill a room or location, preventing oxygen from reaching the fire and quickly controlling it. Some fire suppression systems are designed to emit expanding foam in a fire, and firemen can also use foam tankers and portable foam canisters to quickly apply foam to a fire.