A thermally insulating paint composition including carbon microspheres having an average diameter in the range of 1 to 100 .mu.m. The paint composition including the carbon microspheres can be applied as a primer coating to substrates such a metal, and can be covered with a finish coat of a second paint. The paint system including the microsphere-filled primer can lower interior temperatures when applied to vehicles or structures.
 This invention was made with government support under Contract No. DE-AC05-00OR22725 awarded by the U.S. Department of Energy. The government has certain rights in the invention.