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How Insulation Works

What causes the insulation effect?

The answer is simple and once you understand the fundamentals, the choice of which insulation to use will become clear.


Heat moves is 3 basic ways and always moves form hot to cold.


Convection:  Warm air rises and cold air takes its place.  People often say heat rises which is not true, it is warm air that rises.  Imagine you are standing at a campfire. You see the smoke rising upwards with the warm air and if you kick up the dust just outside of the campfire you see the dust being drawn into the fire.  You are watching a visual effect of the convection process.


Radiant:  Heat energy travels through space and air without giving up its heat energy until it strikes a solid object.  The darker the object the more heat energy that object will absorb, the lighter the object the more heat energy will be reflected off of that object.  Imagine the campfire again and as you are standing there warming yourself, your backside becomes cold.  You turn around so that you can warm your backside, then your front side gets cold so you turn around facing the fire again.  This is an example of how radiant heat works.


Conduction:  Heat will move through objects by conduction, just as electricity moves through a conductor like a wire.  Conduction can be slowed by an insulator just like wiring which has insulation on the outside keeps the electricity inside the conductor and prevents the electricity from shocking us.  Look around you; do you see both a wood object and a metal object such as a desktop and a metal filing cabinet?  Touch the wood object with one hand and touch the metal object with the other hand.  Which object is colder?  You just picked the metal object didn’t you?  If you were to measure the temperature of the both objects they would be the same, but the metal object feels colder because it is a conductor and the wood object feels warmer because it is an insulator.  Try this same test with wood and glass, the results are not as dramatic but the glass feels colder.


Now that we understand how heat moves we can look at what makes a better insulator so that we can keep the heat that we paid for in our home as long as possible.


The insulation Effect occurs when pockets of dead air (trapped air) have been created.  Each pocket will slowly give up its heat to an adjacent pocket until the heat has moved through out the pockets of dead air toward the colder space.  As we have seen with conduction we would not choose metal for insulation.  So what are some of our choices and how do they compare?



Fiberglass Insulation is a well known and widely used product.  It is a man made solid fiber which is basically made from silica and other materials.  The base material is heated to the melting point which uses a tremendous amount of energy, and then the molten material is extruded through small holes where it then cools to form a solid fiber.  These fibers are then treated with a binder (adhesive) to form batts which are then cut to standard sizes, packaged and ready for installation.



  • Low Cost batts can be easily placed overhead between joists and rafter and in stud cavities.
  • A knife and stapler is all that is required to install fiberglass.


  • Each batt has to be cut to size and properly positioned with no gaps or voids.  3%-5% gaps and voids reduce overall effectiveness 35%-50%.  Studies have shown that the actual measured gaps of the installed batts are far greater than the 3%-5%.
  • Glass is NOT a great thermal insulator.
  • Irregular sized and shaped air pockets occur on the outside of the fibers.
  • Drafty, Air easily passes through fiberglass (furnace filters are made of fiberglass).
    • When sheet rock or paneling has to be removed you will see batts that have been installed for several years in wall cavities are dirty the first 2 or 3 feet up from the bottom.
    • Some Fiberglass is now being manufactured to look like its dirty when new so that when it has aged and filtered a lot of air you won't be able to see the difference.
  • Mold will grow on the dirt trapped in fiberglass from the filtering effect.
  • Fiberglass requires raw materials and a tremendous amount of energy to manufacture. 
  • Fibers cause itching, lung and skin irritation.
  • Mice and insects will readily nest in fiberglass insulation and use it for a bathroom.
  • Vapor barrier is required.
  • Poor sound barrier.
  • Fiberglass performance is poor.
  • Fiberglass is not very green for our planet or our budget.


Note: Fiberglass can also be sprayed, bib and blown into cavities and attics.  It improves the performance of fiberglass only slightly because it better fills gaps and voids.  However fiberglass is still made the same way and allows air to move through it.



Cellulose Insulation is a well known and widely used product.  It is a post consumer product made from recycled newspaper and cardboard which is made from wood pulp a natural hollow fiber.  Newspaper is ground in a mill (uses small amounts of energy to manufacture) and treated with a fire retardant.  Some cellulose manufactures use additional materials in their products such as adhesives, fungicides also pest deterrents.



  • Low Cost material that can be applied by spraying into open wall stud cavities and attics.  Custom fit into each stud cavity eliminating gaps and voids.
  • Wood is a great thermal insulator.
  • Hollow fibers provide consistent sized tiny dead air pockets.
  • Eliminates Drafts because air won’t pass through cellulose insulation.
  • Saves space in our landfills.
  • Uses post consumer materials and very little energy to manufacture.
  • Fibers don’t cause skin irritation.
  • Mice and insects will NOT nest in the treated cellulose.
  • Cellulose insulation acts as a fire retardant, dramatically slowing the progression of a fire
  • No vapor barrier is needed.
  • Great sound barrier.
  • With the best cellulose insulation mold is proven not to grow in it.
  • Cellulose proven performer, out performs fiberglass nearly 40%.
  • Cellulose is Very Green for our planet and our budget.



  • Overhead applications are more difficult than fiberglass.
  • Slightly higher cost to install than fiberglass.
  • Requires special equipment to install.



Foam Insulation:  Foam insulation’s are primarily made of 2 different materials, petroleum based or soy based.  Foams use raw materials to manufacture and require a lot of energy to produce.



  • Foam is a great thermal insulator.
  • Foam has tiny cells that form dead air pockets.
  • Air won’t pass through foam.
  • Foam is a proven performer, out performs fiberglass nearly 45%.



  • Foam is substantially more costly than fiberglass.
  • Requires special equipment to install.
  • Requires special personal safety equipment to install.
  • Breaks down over time.  (shrinks)
  • Wall cavities generally are not filled leaving gaps and voids.
    • This is done to minimize labor to cut excess foam that overfills the stud cavity.
    • Most foam installers will tell you "We don't need to completely fill the wall cavity".
    • Do a Google search and look at sprayed foam images, you will see the cavity is not completely filled in.
  • When foam is being applied all other workers must leave the area because of strong toxic fumes.
  • Areas not intended to be foamed require masking and plastic covering to prevent being damaged by foam over spray.
  • Foam is flammable.
  • Foam is a light green for our planet and our budget.
  • Foam is not a great sound barrier.

Conclusion:  Cellulose insulation is the best choice because of the initial cost, impact to the environment, and its performance thermally, acoustically and reducing air infiltration (drafts).  When it comes to insulation, Cellulose insulation is the Greenest of the Green.  However Not all Cellulose insulation’s are created equal.  True the base products would be the same a wood pulp post consumer product but the extras that are added to the product will make a huge impact on the final products performance.  For example Ammonia Sulfate is the primary fire retardant in the less expensive products.  Ammonia Sulfate smells like urine and is corrosive.  A product that has no Ammonia Sulfate but rather uses 100 % Boric Acid is a far better choice.  Boric Acid is a common ingredient found in mouth wash, toothpaste, eye drops and Roach Proof insecticide.  It is not corrosive and is a great fire retardant with the added benefits of insect deterrent.  It is 6 times less toxic that table salt to humans.  It does not smell like urine.  How about an adhesive in the Cellulose?  Products with adhesives will resist settling and will out perform a product that has no adhesive in it because it will maintain its thickness and R-Value.  How about a fungicide in the Cellulose?  Products with Board Defense an E.P.A. tested and approved ingredient will not allow fungi to grow on the cellulose even if the conditions are perfect for fungi growth.  Can I have Cellulose insulation with all these benefits?  The answer is YES you can!  This is why Goodman Heating & Cooling exclusively uses Fiberlite Technologies, Inc products.  We literally install the best insulation in the country.

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