If you're talking about ceramic microspheres, such as the snake oil that's being peddled here:
HY-TECH Insulating paint and insulating house paint additive DIY insulation solutions
I wouldn't believe a thing they say. There is an organization of insulating coatings manufacturers, and hytech's paint additive wasn't even recognized as an IR reflective coating. (Meaning it didn't even work well enough to qualify as an infra red reflective barrier like you see on some foam insulation.
These microspheres have been used as extender pigments in paints for years now, but their purpose has never been to save energy on heating and cooling costs. These spheres are very hard, and as such, provide very good "scrubbability" in paints. Being highly impermeable, they also reduce the propensity of latex paints to stain.
(Yes, it's a real word. "Scrubbability" in paint is the ability of the paint to stand up to hard scrubbing without loosing it's gloss.)
The 3M company is probably the largest US manufacturer of ceramic microspheres. I'd phone them up and ask to speak to someone in their paint & coatings sales division and find out if they've done any investigation into using these microspheres for their insulating ability.
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When reading that 3M web page, a "micron" is a millionth of a meter, or one thousandth of a millimeter. A human hair is about 100 microns in diameter. The smallest thing you can see with the naked eye is 20 to 30 microns across. A red blood cell is about 5 microns in diameter. The black pigment used in paint (which is soot, actually) is about 0.001 microns in diameter, or one nanometer across.
Or, phone up Murelo paints. They use these microspheres as extender pigments in their "NanoKote" line of latex paints:
Maybe ask if anyone using NanoKote has commented on their house feeling warmer or cooler.