The contemporary best practice is expanding spray foam insulation installation. Foam fills the cavities in between the framing studs of the walls and attic. Spray-on foam expands to fills in air gaps, unlike standard fiberglass insulation, which lets air pass through and around it. Even as a house expands and contracts the foam insulation expands and compresses with it. This prevents warm air from escaping through cracks and spaces.

A professional installer has the equipment to cover large areas quickly so that it is more cost effective than doing it yourself, but for small areas and sealing cracks you may choose to do it yourself. For a large space being installed with expanding spray foam insulation, the liquid to sprayed evenly between studs on the inside of the exterior sheathing. The material quickly expands 100 times its volume to fill all the gaps in the stud wall or rafter space. After the foam has set a handsaw is used to smooth off the excess from the framing. The wall or ceiling is now ready for drywall installation.

A better air-tight envelope is achieved by using expanding spray foam insulation in the walls and attic. The foam is non-toxic, high R-value, moisture-proof, fire resistant, and sound damping.

Fire resistant foam insulation contains fire retardant, and some are specifically formulated for fire resistant use.  If you need a fire resistant foam for insulation, be sure to choose one specifically marketed as such.  These products possess a higher degree of fire resistance than standard foam insulation.

Fire Resistant Applications include :
- fire resistant installation of window and door frames
- fire and smoke resistant sealing of connections between walls, ceilings and floors
- sealing of all openings in roof constructions
- sealing of cable and pipe penetrations in walls
- improving thermal insulation in heating and cooling systems

Soudal makes a fire proofing single component PU Foam with non-hazardous propellant and high adhesion to many building materials. SOUDAFOAM FR with CFC-free propellant is a one-component, self expanding, ready to use polyurethane foam with propellants which are completely harmless to the ozone layer. It has a fire rating of up to 229 minutes (4 hours) according to the new European Norm CE 1366-4.

Touch ‘n Seal makes foam sealant and insulating products that contain fire retardants. These foams are intended to resist flaming, and slow flame spread.  However, they cannot stop a fire from spreading indefinitely. Touch ‘n Seal foam is flammable and a fire hazard during dispensing. Do not use around fire or flame, and be sure to extinguish all pilot lights in the area.

ELCH PRO Fire Rated group contains four specialized products for domestic and commercial building applications. FR Silicone and FR Intumescent Acrylic sealants are both tested to BS 476:part 20 and fire rated to 4 hours. FR Acoustic Sealant is also sound tested to a value of 55dBA and is supplied in large volume packs. FR Polyurethane B1 Foam is fire rated between firm, mineral construction substrates and in this application meets the requirements of building material class B1 according to DIN 4102 part 1.

Froth-Pak, although combustible, has a European Class B2 or new Class E fire rating which is equivalent to BS EN11925-2, making it difficult to ignite. The foam’s low thermal conductivity makes it approximately twice as effective as an insulation material as other forms of insulation such as glass fiber, expanded polystyrene and mineral wool.

There are several manufacturers of fire resistant foam insulation products. Be sure to check their fire retardant properties and fire rating specifications so that they suit your purpose.