One alternative reflective insulating measure to radiant barrier foil is the assorted types of spray coatings readily available through paint and insulation manufacturers.
What is spray-on radiant barrier?
Spray-on radiant barriers, officially called "Radiation Control Coatings" (RCC) or "Interior Radiation Control Coating Systems" (IRCCS), are paint solutions, usually of the ceramic variety with metallic flake additives. These added metallic flakes are what manufacturers claim give the coatings their radiant heat reflective properties. The material is most commonly sprayed directly onto the underside of roof sheathing (plywood) from inside the attic.
What are the pros and cons of spray?
Because they can simply be sprayed directly onto the plywood and rafters, spray-on radiant barriers do have an edge when it comes to ease of installation -- assuming the contractor hired to do the coating passes any savings onto the homeowner, or, if doing the work themselves, homeowners have easy access to the necessary equipment.
When it comes to performance, however, the edge ends there for spray-on radiant barriers.
In 2006 (and revised in 2010), a study done for RIMA International (Reflective Insulation Manufacturers Association International) showed that only six of the sixteen coatings tested met the industry standard of thermal emissivity required to be classified as a reflective radiant heat barrier (1). This standard was set by the American Society for Testing and Materials (ASTM) specifically for spray-on coatings themselves, and requires a thermal emissivity of .25 or less (meaning at least 75% of radiant heat is reflected).
What the study found is that spray-on radiant coatings are not efficient barriers against radiant heat. Some even had an emissivity of as high as .90, meaning only 10% of radiant heat was reflected. These are the numbers of conductive not reflective insulation.
How does it stack up to radiant barrier foil?
The radiant barrier foil product line offered by Innovative Insulation, Inc. has minimum emissivity properties of .05. That means more than 95% of radiant heat is reflected. And that means, quite simply, radiant barrier foil is a far more efficient option than spray-on coatings.