Foam insulation boards, also known as rigid foam insulation, are an extremely effective way to insulate buildings and improve energy efficiency.
But how exactly do these lightweight boards manage to slow heat flow and save on energy costs? The science behind foam insulation gives us the answers.
What is Foam Insulation Made Of?
Foam insulation is made by converting liquid plastic resins into foam through a chemical process. Different types of plastic resins can be used when manufacturing them. The most common ones are mentioned below.
- Polyisocyanurate (polyiso) – Contains a thermoset plastic with a cellular structure blown using hydrochlorofluorocarbons (HCFCs) or pentanes.
- Extruded polystyrene (XPS) – Made from solid polystyrene blown into foam with hydrofluorocarbons (HFCs).
- Expanded polystyrene (EPS) – Solid beads of polystyrene are first expanded using steam and then molded into rigid foam boards.
- Polyurethane – Starts as a liquid blend blown with a foaming agent into solid insulation.
The resins used give the foam boards strength and rigidity. Moreover, the blowing agents generate millions of tiny air pockets within the foam. It is responsible for offering excellent insulation capabilities. Additives like fire retardants may also be included.
How Do Foam Boards Slow Heat Flow?
Foam insulation works by slowing conductive and convective radio flow. The millions of air pockets trapped within the foam significantly reduce its thermal conductivity. As a result, it becomes harder for heat to flow through.
While still air is typically a good insulator, at very small scales natural convection causes some heat transport. But the air pockets in foam insulation are so small (1/16th inches or less) that air molecules cannot set up free convection currents. This severely limits heat transfer through the foam.
Finally, small closed-cell structures in the foam reflect radiant heat instead of absorbing it. This causes radiative heat from sunlight or warm objects to bounce around rather than transmitting through the insulation easily.
The combined effects make heat flow extremely slowly in foam boards. Thermal testing shows R-values (a measure of resistance to conductive heat flow) from R-3.5 to R-8 per inch depending on foam type and density. Foams formulated with specialized infrared-reflective facers can reach even higher R-values.
Improving Building Envelope Air Sealing
Foam boards can also provide excellent air sealing. Air gaps in the building envelope let in outside air. This forces HVAC systems to work harder to heat and cool the building. According to the EPA, air sealing and insulation can reduce heating and cooling costs by up to 30% in older buildings.
Foam boards come in large sheets. That’s why they can span gaps between wall studs and rafters easily. Professional spray foams can fill even more cracks and spaces. The result is fewer pathways for air to leak through framing cavities. Combine foam boards with caulks, tapes, and weather stripping on seams and openings to maximize air sealing.
Moisture Protection in the Building Envelope
Properly sealed foam insulation also protects against moisture drive. Condensation can occur when warm and moisture-laden air contacts a cold surface. Over time, this moisture accumulates in wall and ceiling cavities, leading to material degradation, mold growth, and huge energy losses.
InsulationPoint told our reporter that foam insulation resists moisture absorption and forms a protective layer over sheathing and framing. Closed-cell spray foam insulations are even vapor retarders, as they significantly obstruct water vapor diffusion. Retarding moisture drives building materials dry, preventing structural issues and energy waste from excess humidity.
Maximizing Long-Term Thermal Performance
Unlike some insulations, the structure and insulating capacity of foam boards remains stable over time. As foam has low moisture absorption, it resists settling and decomposition from humidity or water exposure. Protected from sunlight beneath finishes, foam retains initial R-value year after year.
Additionally, foam insulations are inert once cured, meaning they do not provide food value to pests, rodents, or mold. Plastic foams won’t react with acids or alkalis either. This lifecycle stability makes foam a smart, long-term insulation investment for buildings. Long after fiberglass batting or cellulose insulation has degraded, foam keeps insulating at peak performance.
Structural Rigidity in External Insulation Finishing Systems
External insulation finishing systems (EIFS) take advantage of foam board rigidity to insulate and improve buildings. By adhesively attaching foam insulation to exterior walls and finishing over it with mesh-reinforced base coat and acrylic finish coat, a durable and decorative surface is created while improving thermal performance.
The underlying foam layer adds R-value while remaining sturdy enough to support finishes through all seasons. Foam choices like EPS or polyiso have the compression strength to withstand wind, precipitation, and other environmental factors once installed. The resulting EIFS façade resists cracking and detachment better than using other less rigid insulations.
Understanding Fire Safety Concerns with Plastic Foams
With so many advantages, why doesn’t every building utilize foam insulation? One potential downside is that foam plastic insulation tends to be flammable to some degree once ignited. Materials like EPS foam in particular burn rapidly and release intense heat when not shielded by an adequate thermal barrier.
However, manufacturers formulate commercial foam boards to be fire-retardant. Fire-rated products often pass standardized combustibility tests like NFPA 285 and CAN/ULC S101. This ensures foam insulations meet fire safety codes for use within wall assemblies and ceiling spaces. Always check applicable fire testing data before specifying foam insulation.
Additionally, cover any interior foam board insulation with a minimum of 1/2″ gypsum wallboard or another approved thermal barrier. This protects building occupants by preventing flame spread and smoke development. Follow all local fire and building codes to use foam safely.
The High Performance of Foam Insulation Boards
From polyurethane spray foam to extruded polystyrene sheets, foam insulation stops energy waste thanks to its cellular structure trapping air to form an incredible insulating barrier. Strong, rigid, and moisture-resistant, foam insulation keeps working for the long run. And though flammability requires special attention, compliant fire-rated foam is safe for inhabitable spaces.
Combine these inherent advantages with reliable R-values between R-3.5 and R-7 per inch, and foam becomes an essential component for energy-efficient homebuilding. Tight, well-insulated building envelopes are crucial to meeting strict energy codes and construction standards moving forward. Click-lock rigid foam boards provide quick, uniform insulation for roofs, walls, foundations, and more – all while advancing sustainability.