What Makes Spray Foam Insulation so Effective?
The only proven solution to fixing a hot, humid South Florida house.
It’s no mystery that spray foam insulation has incredible thermal properties compared to traditional fiberglass or blown-in insulation. In this very short article we'll explain why.
In addition to being an approved air barrier, spray foam insulation blocks all three forms of heat transfer. Let’s dive more into why foam insulation is the most efficient insulation product on the market. But before going further, it's good to know the meaning of R-value, which is often discussed when comparing various insulation products.
Simply put, R-value is a means of measuring how well an object resists conductive heat flow. In our case, the amount of insulation that you put in a floor, wall or ceiling. This is a very one dimensional way of viewing a complicated subject. There are also two other forms of heat transfer that aren’t being taken into account with the R-value measurement, radiant heat transfer and convective heat transfer. So we now know that we have 3 known forms of heat transfer in total to mitigate when discussing insulation in our building or home:
Conductive, Convective & Radiant Heat Transfer
Let’s start with...
Conductive Heat Transfer.
The transfer of heat from one object to another by direct contact. At this time, this is the only form of heat transfer that is factored in the current calculation to determine an insulation product's R-value.
An excellent example of conductive heat transfer is a clothes iron or a pot being heated on a stove. The heating element is in direct contact with either clothes or the pot causing the clothes and water to get hot.
So why is spray foam insulation superior to other insulation products at preventing conductive heat transfer? We first have to understand that spray foam insulation is actually not foam at all, but rather a two-part thermoset plastic, compromising of millions of tiny cells that are either filled with air (open cell foam) or a blowing agents such as 245FA or Solstice (closed cell foams). Spray foam “plastic” insulation contains polymers and isocyanates that cross-link together during the curing process to form an irreversible chemical bond. This process eliminates the risk of the product re-melting when heat is applied or when its subjected to even the harshest of environments.
The most common consumer products made from thermoset plastics include food and beverage coolers, styrofoam cups, packing foam products and of course various forms of spray foam insulation products. Thermoset spray foam insulation located on the inside of a food & beverage cooler. Fun Fact: The smooth plastic inner liner is actually a thermoplastic, which can be heated and remolded.
All thermal energy is transferred by vibrating molecules colliding with each other. This process happens very slowly with plastics due to their chemical makeup. This is due to plastics (spray foam insulation) having the cross-linking bonding throughout the structure. Therefore making plastics (spray foam insulation) a poor conductor of energy. This is why a Yeti Cooler (which is insulated with spray foam) can keep ice in its solid form for so long or that a sytrofoam coffee cup prevents your hand from burning. This property is true with both heat and electricity as it doesn’t have a proper path to transfer energy from one bond to another being it’s cross-linked nature.
These bonds are weak in comparison to other chemical bonds such as metallic or ionic bonds. As such, polymer bonds breakdown instead of letting energy pass through them freely in the form of heat and/or electricity, being they don’t have that much capacity to handle or transfer energy from one bond structure to another. This effect is even further compounded in the case of spray foam insulation, by the fact that trapped pockets of air or other inert gases such as 245fa boost this molecular effect. The atmosphere, as in the air we breathe or 245fa in the case of closed cell foam, are some of the best insulators available, these empty voids or air-filled pockets within the spray foam cell structure help further improve the overall thermal efficiency. Which brings us to our next form of heat transfer...
Radiant heat transfer
Radiant heat is simple heat transfer through an infrared source. Examples of radiant heat transfer are heat felt from sunlight exposure and heat from an infrared home heater. Did you know that Earth receives radiant heat transfer from the sun, located 92.96 million miles away? That's one powerful energy source!
Spray foam insulation the most effective insulation at mitigating radiant heat transfer due to foam insulation having a reflective, low-emittance surface. Additionally, most spray foam products are light-colored which aids in the reflectiveness of radiant heat transfer. White, which is the color of most spray foam insulation, has the highest solar reflectance of all the colors. Think of a hot summer day and sitting in a black car versus sitting in a white car. There is a drastic difference in interior and exterior temperatures due to radiant absorption, or lack thereof in the case of the white car. This brings us to our last form of heat transfer...
Convective heat transfer
Convective heat transfer is the movement of heat flow through fluids, either in liquid form or atmospheric (through air movement). Examples of convective heat transfer would be from convection ovens, blow-dryers, or warm water from the shower passing over your body. Inside of convection oven or blower. The heating elements produce radiant heat first then an internal fan pushes air over the heating element to create convective heat flow. A shower allows hot water to hit your body which heats your body.
The way that convective heat transfer impacts homes is through the commonly installed attic soffit vents, ridge vents and/or gable vents. The purpose of these vents is to allow air to enter and exit the attic to theoretically cool off a hot attic space. The problem is that this happens in an uncontrolled manner and if not very effective. During Florida's hot summer months, hot, humid convective heat flows enter the home through these vents causing an excessively hot attic. While in cool winter months (mostly seen in other climate zones such as the Northeast, Midwest, and West), conditioned convective heat is released into the attic causing conditioned air to be wasted.
The main advantage spray foam insulation has over other insulation products it that it provides a complete air barrier. Spray foam insulation has the ability to stop all convective heat transfer by effectively air sealing every areas it is applied to. This effectively stops hot, humid air from entering attics in the summer top and stops cool, outdoor air from entering attics during the wintertime.
In addition to significantly reducing convective heat transfer, spray foam also eliminates any potential dew points from moisture-laden air that can create condensation which has the potential in creating conditions that cause mold and mildew within the home structure as well as the internals of HVAC components. Attics with spray foam in the roof deck no longer reach temperatures of 100, 110 or even 120 degrees Fahrenheit during the summer which eliminates the potential for condensation to form on the surface of duct work, return/supply grilles or the HVAC unit itself. An attic with spray foam installed will be within 5-10 degrees of the rest of the home!
That is why energy-conscious architects, builders and homeowners choose spray foam to insulate their homes. Spray foam is very effective at keeping conditioned air inside the home and unconditioned air outside the home, thereby eliminating all convective heat transfer. By doing so HVAC units will no longer have to work as hard to keep a house cool in the summer and warm in the winter, which can result in up to a 50% or more reduction in heating/cooling costs over time! Your A/C system will also work less hard to keep your house cool as well as being in a more temperate environment which increases the life of your HVAC equipment. Best of all, your home will be comfortable, energy-efficient and quiet!