<；P>；PROBLEM TO BE SOLVED: To provide a heat insulating agent comprising surface-treated hydrotalcite excellent in heat insulating property, transparency, and acid resistance, and to provide a method for producing such a heat insulating agent and the use of the same to an agricultural film. <；P>；SOLUTION: A coating comprising hydrous silica is formed on the surface of each hydrotalcite particle by adding a water-soluble silicate to a slurry including hydrotalcite particles at a temperature within the range of 60-100°；C, and then adding an acid to the slurry. The heat insulating agent comprising hydrotalcite having a coating of dense silica on the surface in an amount of 1-50 wt.%, obtained by subjecting the resulting slurry of hydrotalcite to hydrothermal treatment at a temperature within the range of >；100 to 300°；C, is provided. Further, an agricultural film containing such a heat insulating agent is also provided. <；P>；COPYRIGHT: (C)2006,JPO&NCIPI
