With this past summer’s heat in the low three digits, many of us are sweating electric bills in the high three digits. As homeowners search for ways to rein in energy costs, new technologies and financial incentives are as welcome as a cool breeze.

Heating and cooling account for 50 percent to 70 percent of the energy used in the average American home, and adding wall insulation is one of the most effective weatherization steps homeowners can take. If your home is as little as five to 10 years old you likely have one of America’s 46 million under-insulated homes, according to the Harvard University School of Public Health.

Insulating existing homes is no longer the major construction project it once was when it involved tearing into walls to insert fiber batting and spray-on foam, or cutting large holes to blow in loose-fill insulation.

Eco-friendly formulations of foam insulation can now be injected into wall spaces entirely from the home’s exterior and is one of the most effective forms of weatherization. A government tax rebate makes adding insulation an even more attractive choice to slow the electric meter.

New choices in foam insulation allow injection through the outside wall via small holes drilled in the mortar spaces between the brick or other exterior siding. This process involves drilling a row of three or four small ¾” holes within each stud cavity.

The injection process begins at the bottom hole. Air is allowed to escape through the upper holes as the foam gradually replaces the air in the wall. This foam insulation has the consistency of shaving cream when it first leaves the injection nozzle. The creamy consistency allows the foam to flow into the wall and work its way around any existing insulation. As the wall fills, the injection nozzle is moved from the lower holes to the upper holes until it is finally capped off at the top plate. This process continues around the house perimeter until the walls are all filled.

Within one minute of injection, the foam solidifies and then cures fully within a day. After all walls are filled, the crew mixes mortar and fills the injection holes with matching mortar or inserts wooden plugs leaving little evidence of the insulation process.

And while foam insulation usually costs more than traditional batt insulation, foam forms an air barrier. This can help eliminate other costs and tasks associated with weatherizing a home, such as caulking, applying housewrap and vapor barrier, and taping joints.

Foam insulation has usually been reserved for new homes because there wasn’t a cost-effective way to get the foam into the wall cavities of existing homes. Contractors tried their best, drilling holes in drywall near the ceiling and ladling “pourable” versions of these expanding foams into the airspace within the wall. This method worked, but it was slow, messy and required costly repairs to patch holes and cracks in the drywall. While some homeowners could afford to upgrade to foam insulation, the additional costs for drywall repairs and repainting pushed it outside the range for many others.

There are several foam insulation products on the market today. Some, such as polyurethane and urea formaldehyde foams, have drawbacks such as containing toxic chemicals, shrinking as the foam ages and deterioration of insulating value. Other products have been withdrawn from the market, and some are just now becoming generally known by both construction professionals and homeowners.

Some non-toxic, highly effective injectable foam insulation products are entering the market, although they aren’t as well-known as the older, traditional types of insulation. And in the case of one such product, RetroFoam, confusion about its content resulted in it being banned in Canada despite the manufacturer’s protests. There’s even a soy-based foam on the market in some parts of the United States.

A proprietary hybrid injectable foam insulation product marketed as Tripolymer® or HomesulateTM, is making inroads across the country as installers establish their business territories. Created in 1966 by the C.P. Chemical Co. of New York, this material was originally designed for use as a fire-resistant thermal and acoustical insulation in commercial and residential structures.

In 1975, the company expanded and refined its material with the help of the U.S. Department of Energy, which chose it as one of three products out of 7,000 candidates to assist in further development. After three years of intense research and testing, Tripolymer 105 greatly surpassed all expectations.

It is now available to retrofit homes and involves an economical process that enables crews to inject non-expanding foam insulation into wall cavities that will bond with whatever existing insulation may be in the wall.

Some customers have saved up to 50 percent on their energy bills and the process qualifies (at least through the end of 2010) for up to $1,500 in federal tax credits. Many electric utilities offer additional cash rebates for weatherization projects such as adding insulation. Cost recovery from energy savings, rebates and tax credits can be a matter of a few years or less.

In addition to energy savings, many wall foam insulation products offer increased fire resistance and noise reduction from outside sources.

Insulation products are rated in terms of thermal resistance, called R-value, which indicates the resistance to heat flow. The higher the R-value, the greater the insulating effectiveness.

The new breed of foam insulation products provide impressive R-values. They vary somewhat, but the Homesulate formulation has the highest R-value of any retrofit insulation at 5.1 Rs per inch. That’s a full 45 percent greater than blown-in fiberglass and 30 percent above the best blown-in cellulose. C.P. Chemical’s product delivers R-values of between R-17.8 and R-28 depending on a home’s construction.

Ask anyone living in a home with spray foam insulation in their walls. Their energy bills are lower than their neighbors with standard insulation; the home is more comfortable, with consistent temperatures from room to room; and they don’t notice the barking dog next door.

Carolee Kamesch is president of Prestige Designer Homes ( http://www.PrestigeDesignerHomes.com ), a custom home-builder in Dallas, and owner of Homesulate of North Texas ( http://www.FoamMyWalls.com ), a foam insulation installation company. Among other certifications, she is a Certified Green Professional (CGP) and serves on the board of directors for Green Built Texas.