Both the radiant barrier spray paint and the radiant barrier foil "Reflect" or will not "Emit" attic radiant heat. The best available radiant barrier paint will reflect about 75% of the radiant heat transfer and the radiant barrier foil will reflect about 97% of the radiant heat transfer. Radiant Barrier Foil is actually the "Best" radiant barrier. What is Radiant Barrier Paint? Radiant Barrier Spray Paint is essentially "liquid foil". All Radiant Barrier Paints are different, but basically pure aluminum is ground into a powder and put into a clear paint. Once the clear paint dries the aluminum powder forms a layer of aluminum. The best radiant barrier spray spray is only available to commercial contractors, and is an environmentally safe, water-based low-e paint called HeatBloc-75, Radiance e.25. or Lo/MIT. When the spray is installed CORRECTLY it will reflect about 75% of the radiant heat. Second, the paint is being applied with the correct coverage (many spray contractors put it on too thin or too thick). Finally, there are some contractors (even large ones who advertise heavily) that will cut the paint with WATER to extend the coverage. This is called "Cutting" and it is cheating to cut costs. As a result, the TRUE EFFECTIVENESS of radiant barrier paint installed by many contractors is really only about 15-40% reflectivity. The typical consumer can't tell the difference between a good installation and a poor job without testing.The fumes are noxious, you MUST use a VOC Respirator, you need a high-end airless spray rig, know what size spray tip to use and the proper pressure to get correct coverage and eliminate cloggage. Most people who try to do it themselves will actually blow too much paint and the material cost alone wil be over .30/ft. Painting with a roller is impossible since there are thousands of nails sticking through the roof deck and using a brush would take forever. Why Use Radiant Barrier Foil? Basically you are counting on the PRODUCT to do the work not a PERSON. If the foil is installed somewhere between the roof or rafters and the insulation it WILL reflect 97% of the radiant heat. This is indisputable - Radiant Barrier Foil works! This is the difference between Quality Assurance and Quality Control. You can ASSURE that reflective foil will work. You can only HOPE that the Radiant Barrier Spray is installed correctly. We no longer install radiant barrier paint. We only install radiant barrier reflective foil insulation with our professional installers.