When you are at the home center shopping for insulation, all of those giant bales of fiberglass, rigid foam, and even denim can look daunting. So, when you see a product like Reflectix, it seems to be a relief to all of that hassle. It's small, tidy, clean, and best of all, it offers thermal-blocking R-values of up to R-27.
As it turns out, Reflectix is not a competitor to fiberglass. It's a different kind of insulation for different applications. You'll still want to install fiberglass, foam, denim, or rockwool in your home's large wall and ceiling cavities. But Reflectix can supplement those types of dense insulation with reflective insulation to provide a more total, insulated home.
What Reflectix Insulation Is
Found in the insulation aisle, Reflectix comes in tightly spooled rolls of shiny, reflective, foil-look insulation that resembles bubble wrap. There is no metal content; it is all plastic.
Reflectix is a little thicker than a quarter-inch (5/16-inch). It's very lightweight (about 1-1/4-inch per square foot). It's flexible enough to bend back on itself.
Reflectix can insulate tight spaces where you cannot put thick insulation or where other types of insulation are not appropriate.
Reflectix is a reflective insulation. So the stated R-values on the Reflectix label are valid only when the insulation is applied in a certain way.
For example, the R-6.1 masonry value stated on the Reflectix label is good only if you provide two 3/4-inch airspaces. One airspace must be between Reflectix and the masonry wall and another space between the drywall and the Reflectix.
Reflectix's stated R-14 R-values for exterior walls are good only if the Reflectix is paired up with R-13 fiberglass batt insulation.
If you do not provide air space, Reflectix has less insulating value. Reflectix states this in its sales literature:
No Air Space = No Reflective Insulation Benefit. (An R-1.1 is provided from the product itself for the Reflective/Double Bubble material.)
Where to Use Reflectix
Reflectix lets you insulate spaces that might ordinarily go uninsulated because it would be prohibitive to insulate them with fiberglass.
You might have a cold workshop with heat escaping through the roof. Stapling a layer of Reflectix along the rafters will cut down on some heat loss and stop air infiltration. If you cannot or are unable to insulate the ceiling with fiberglass or foam, Reflectix is an alternative. As a nice byproduct, its reflective surface would give your shop more ambient light.
Reflectix can help with any areas where cold air is blowing into your house. While caulking is the recommended procedure for this, there may be situations where a large expanse of Reflectix will stop airflow.
Because Reflectix is so flexible, it can be wrapped around pipes and heating vents. If your local code allows, Reflectix can be wrapped around the water heater as a thermal blanket.
Some homeowners face the inside of their garage doors with Reflectix to help insulate these spaces for use as workshops.
Reflectix can act as housewrap, too. Behind brick, Reflectix has an R-value of R-3.4. Behind aluminum or vinyl siding, its R-value is R-2.5.
So, even though Reflectix functions best with airspaces, there are some applications where it is impossible to add airspaces, such as around pipes, vents, and water heaters.
Reflectix can be used as basement ceiling insulation when precisely stapled to the centers of the floor joists above. The product must be applied tightly, with room for airflow.
One benefit of using Reflectix over fiberglass insulation is that Reflectix resists mold and mildew well. If it does develop mold and mildew, it can be cleaned off. When fiberglass insulation becomes moldy, it must be discarded.
When Should You Buy Reflectix?
Reflectix can be used as wall cavity insulation—but tacking it to the centers of the studs in each cavity is a laborious process. Traditional fiberglass insulation is easier and faster, and it will insulate better.
The key to using Reflectix properly is to understand how reflective insulation works in the first place. The Reflectix site provides a great range of information about this and about how it differs from other types of insulation. The product is more like a Thermos jug, in that it reflects heat back, rather than mass insulation such as fiberglass.