Comparing Popular Insulations

When you start a project on your home, you want the best product for the lowest price.  Nobody installs insulation in their attic because they like things that are fluffy.  You want insulation because it lowers your bills, keeps your family warm in the winter and cool in the summer, and all the other great reasons to insulate your house.

But what makes one type of insulation better than another.  What’s “best?”  Let’s look at effectiveness, safety, and cost.  All modern insulations have a 100+ year life expectancy.

Let’s hear it for spray-foam, the sexiest insulation around.  Inch-per-inch, closed-cell spray foam is the best insulation out there (that is reasonably available to consumers).  To reach the insulating value of an inch of closed-cell foam, you would need at least two inches of other, cheaper insulations.  Properly applied foam will expand around obstacles, eliminating insulation-voids. It adheres to clean surfaces, keeping the insulation in contact with the surface it’s insulating, and it creates a very effective moisture and air barrier.  Modern polyurethane foams are a safe, long-lasting, and proven method for insulating.

However, spray-foam is usually the most expensive insulation out there.  It can’t be injected into finished walls – that’s a different product.  If you don’t plan to tear down drywall, your spray foam is mostly limited to the attic and basement.  Open cell spray foam is less expensive than closed-cell, but it does not have the same moisture and air-blocking properties.  Any spray-foam needs to be covered with a thermal or ignition barrier and cannot be left exposed in accessible attics and basements.

Rigid Polystyrene Foam Board comes in two flavors: EPS and XPS depending upon whether the foam is Expanded like tiny foam balloons all glued together like Styrofoam, or eXtruded like board insulation being squeezed out of a Play-Doh Fun-Factory.  You might think of either of these as “Pre-cast” spray-foam.  It’s foam insulation, but it arrives on the truck in big sheets like plywood.  Inch-per-inch, we still can’t beat urethane-spray-foam, but we’re still better than blown or rolled insulation.  Rigid foam boards are great at stopping air-flow if they are properly installed and the seams between pieces are well sealed.  Material costs for rigid foam is much lower than spray-foam, but the labor costs are much higher.  Foam boards can often be used in conjunction with blown or batt insulation to provide an effective air-barrier to stop wind-washing.   Any Styrene foam board needs to be covered with a thermal or ignition barrier and shouldn't be left exposed in accessible attics and basements.  This includes pink-board, blue-board, Styrofoam, etc..  Dr. Energy Saver dealers across the US also offer SilverGlow -- a graphite infused foam board that boosts EPS performance.  (but you can't write with it, despite the graphite!)

Polyisocyanurate Foam Board is a mouthful a little different.  Unlike the styrene boards, it’s a “thermoset” foam, and therefore is more fireproof than the alternatives.  In fact, it’s the only foam board that’s allowed to be left exposed in accessible spaces.  Not only that, but it’s got the best insulation levels per inch of any foam-board, coming close to that of spray-foam.  Guess, what?  It’s also more expensive than other foam boards!

Blown cellulose insulation has come a very long way since it first came into fashion.  Cellulose is basically paper.  People have been using newspapers and paper to insulate since the earliest days of modern home insulation.  The problems with the old methods were many.  Old wrinkled pieces of paper, stitched together with cotton twine don’t provide much insulation.  Over the years, they settle, rot, or become habitat for mice.  Blown shredded paper from "years gone by" would run into the same problems.  How did these problems get fixed?  Borate – you may know it as Borax.  It makes the cellulose longer lasting, pest free, and more fire-resistant that most any other insulation out there.  It performs significantly better than fiberglass.  The challenge with any loose-blown insulation is wind-washing.  If air can travel through the insulation, then it ceases to insulate.  A combination of foam or caulk should be used to seal up any air-holes before blowing in insulation.

Cellulose can also be densely packed into enclosed spaces such as wall cavities.  By packing the insulation in tightly it effectively blocks drafts and convection currents within the wall. 

Fiberglass has the lowest insulation value per inch of any typical insulation out there when measured in the laboratory.  In the real world of attics, wind-washing, and lazy installers, the performance is much worse.  Like any blown or batt insulation, it will settle over time and with humidity.  Unless it’s treated with formaldehyde, the binding agents in fiberglass can mold.  The largest benefit to using fiberglass is the cost.  In the right situation, it can be the right answer, but it should not be the go-to solution for every problem.