Choose the Right Insulation

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By Energy Circle Staff - August 18th, 2009

Now that you know all about R-value, consider which materials and application are most appropriate to your needs.

Part A: The Goods

As we've examined the range of insulation options available, it's become clear that homeowners have more factors to consider than ever. As with most enterprises, knowing what your priorities are will help you select the product and installation process that will give you the results you need.

  • Where you need insulation: retrofitting an attic is a lot different than insulating unfinished walls in a new house, and may require a different type of insulation. Consider, too, if there is the possibility of moisture contact. Closed-cell foam will still be effective if it gets wet, while the R-values of cellulose or fiberglass will be compromised.
  • Who will be doing the installation: some types of insulation are easier to install than others. You should hire a contractor to install spray-foam, for example.
  • Where you live: how to insulate your home most effectively will depend on the climate you live in, in respect to ideal R-values and ROI of insulation types.
  • Sustainability and environmental impact: if you're looking to make your house more "green," you might consider insulation made from recycled materials.
  • Health and safety: Some insulating materials contain toxic chemicals, some are all-natural, some are more fire-resistant than others. Take a look.

Common Insulation Types: Consult this list before speaking with your contractor, and be sure that you are making the choice that makes sense for your home and your health.

Batts and blankets: Fiberglass batts and blankets are the most common type of insulation in U.S. homes, but not necessarily the best. Batts are pre-cut, blankets come in a big roll. Cotton batts or "blue-jean insulation" - a non-toxic alternative to fiberglass - are also available, if slightly hard to come by. The advantages and disadvantages below refer specifically to fiberglass batts and blankets, by far the most common.

  • Advantages: Fire resistant, won't settle over time. Good for retrofitting an attic if there aren't a lot of obstructions; just lay it on top of the existing insulation, taking care not to leave gaps or skimp out around the eaves. Fiberglass is inexpensive (compared to cotton batts, spray-foam or rigid insulation), and is comparable to cellulose in terms of R-value.
  • Disadvantages: Can leave holes and gaps where air can circulate, reducing the R-value, or where condensation can occur, also reducing R-value. Fiberglass particles pose a health threat during installation. It takes around 10 times as much energy to produce fiberglass insulation as cellulose, so it's not especially friendly to the environment. You wouldn't be able to retrofit walls with batts without removing the drywall.

Loose-fill (cellulose insulation): Can also be wet-sprayed (applied with a water-based adhesive).

  • Advantages: Cellulose is made with up to 80% recycled material (shredded newspaper, mostly), it uses less energy than fiberglass to manufacture, it's non-toxic, inexpensive, more effective than batts at sealing air leaks as well as nooks and crannies, flows around wall studs to increase the R-value of the entire wall, and it's highly flame-retardant. It's also easy to retrofit walls with dry-fill cellulose by cutting a small hole (which will need to be patched, obviously) in between each stud at the top of the wall and blowing in the insulation. You'll also want to remove a piece of drywall at the bottom of the wall to make sure the cellulose has made its way all the way down. Cellulose is also good for retrofitting attics; if it's distributed evenly you can be sure there are no gaps in the thermal barrier.
  • Disadvantages: May absorb moisture, and can settle over time if not installed properly, both of which reduce its R-value. It's heavier than fiberglass, so it may cause ceilings to sag.


  • Advantages: Foam expands, so it seals up leaks and gaps better than either cellulose or batts. It's easy to install in tight spaces, and can be installed in wall cavities without removing the drywall. Note that there spray-foam comes in all shapes and sizes (and prices, R-values), but the two general categories are closed-cell and open-cell. Closed-cell foam has a higher R-value (about 6R per inch), but is more expensive than open-cell (which is about 3.5R per inch). For an equivalent R-value, open-cell will generally be less expensive. The high R-value-per-inch of closed-cell foam makes it a good choice if you have limited space; it also prevents moisture transmission better than just about any other insulating material.
  • Disadvantages: Foam is pricier than most other insulating materials to begin with, and it will need to be installed by a spray-foam contractor (no do-it-yourself option), raising the price even more. It also may release greenhouse gases during application, so it may not be the greenest option. Once installed, spray-foam is not a health hazard.

Reflective Insulation and Radiant Barriers:

  • Advantages: Reflective insulation and radiant barriers serve primarily to reflect radiant heat, but do little to prevent heat transfer through convection. They're highly useful in southern or warm climates where the main objective is to keep solar heat out of the building. They look like a big sheet of foil, and serve primarily to block solar heat, even though they're applied internally. Here's how: the sun heats the materials on a roof, for example. These materials, now hot, transfer heat through convection (heat moving through the material) and through radiation (heat emitted directly from material). The radiant barrier, which you could install by laying it on top of existing attic insulation, or by attaching it to the underside of the rafters, blocks the radiant heat, reflects it back into roofing material and keeps it out of your living space.
  • Disadvantages: Doesn't prevent convective heat transfer - so it won't keep the heat inside in the winter. Reflective insulation does include a thin layer of material to prevent heat transfer through convection, and so has a small R-value (a radiant barrier has no R-value). Reflective insulation and radiant barriers thus serve as a supplement to bulk insulation (i.e. cellulose, spray-foam or fiberglass batts), but will not suffice on their own, particularly in cool climates.

Rigid Panel Insulation:

  • Advantages: Rigid insulation has a high R-value per inch, so it's a practical solution for a high R-value where space is limited.
  • Disadvantages: They can't be retrofitted into existing walls without removing the drywall, and are susceptible to the same air-leakage problems as fiberglass batts and blankets. They need to be meticulously installed to limit gaps and air leaks, and they're slightly more expensive than alternatives.


On the advice of our home energy auditor - recommended by our Energy Circle friends - we just had the basement & crawlspaces under our ancient (late 1700's) house sprayed with foam insulation. We look forward to a cozier house next winter & a lower heating bill for years to come. But a word of warning for others considering this installation. Have it done in warm weather when you can air out the house and keep your family outside until the foam sets. The smell didn't linger long but the day of the installation our house was toxic and we temporarily abandoned ship. Posted by Jenny M on Apr 1, 2010 8:11am

Thanks for the comment, Jenny.  Good point.  Though think about the savings you could achieve by tackling those holes as soon you find them!  We're looking forward to hearing how much your insulation job helped your lovely, albeit drafty, home's sense of comfort & efficiency.

Posted by Lisa on Apr 1, 2010 8:51am
Spray-foam: ... Disadvantages:... It also releases greenhouse gases during application (HCFC's or HFC's), so it's not the greenest option. The above comment about spray foam is no longer true. Spray foam is now considered 100% green and gives off no green house gases Posted by John Hammond on Jun 28, 2010 11:19am
question to John Hammond: Are you sure about 100% green? I have heard around 98% but understand there is still some "un-green" components in even the best of them (not including production and distribution processes) . I know there have been improvements in the product, like replacing most of the petroleum with vegetable oil and using non-VOC blowing agents, but like everything else it is imposible to be 100% perfect for the environment. Is there a particular company product or brand name you can share that can claim 100% green? I still think 98% is pretty darn good though. Posted by Robert on Jun 28, 2010 1:09pm

Great comments!  In the second paragraph of my reply here, I figured, what the heck -- my thoughts about whether foam is good or bad for the environment is up for all to read.  Your comments here or there are warmly welcomed, no matter how much you disagree with me :-)

Posted by Tom Harrison on Jun 28, 2010 3:54pm
When discussing spray foam, you say it can be installed in wall cavitied without removing the wall board. Are you referring to one specific type of foam? Over the years I've talked with several installers of foam, and every one has said they can't retrofit into an old house like mine unless we strip the outside walls. Thanks for an informative site! Posted by Alan M on Jul 2, 2010 9:13pm

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Posted by monmouth university on Sep 22, 2013 1:01am

 I'm no expert, but I did find this link, suggesting that with care, existing, enclosed wall cavities can be filled with foam.  I think it's not a do-it-yourself affair -- the right foam that expands the right amount would be needed.  Given cost, blown-in cellulose is probably the preferred method, in most cases.  I have had cellulose installed in my house both from the outside and from the inside.  The former required removal of the clapboards; the latter a suitably placed 2" hole in the plaster.

Posted by Tom Harrison on Jul 3, 2010 2:08pm
Very good information , I'm in the field and agree with what you have written. Posted by Tom on Aug 28, 2010 7:05pm
we've installed all these different types of insulations. As written all have advantages and disadvantages in Phoenix, az we find the radiant barrier is the best bang for the dollar. Posted by Anonymous on May 21, 2012 10:40am

Thanks for the post and I am agree with your point that choosing the right place for insulation is essential if you have new construct house then you need to insulate. myself I have insulated my house.

Posted by Petson on Dec 2, 2014 5:56am

I want to find a natural insulator for my house, we're getting rid of the fiberglass. We have young kids running around, and I don't like the fiberglass in the air. I'm sure there is a better option for us out there, especially in the attic. The house could be more energy efficient as well, so we'll be taking that into consideration.

Posted by Ashley on Apr 9, 2015 8:25am

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