Abstract: This invention relates to insulating sleeve compositions comprising (1) a major amount of hollow aluminosilicate microspheres, and (2) fine silica. The sleeve compositions are used to form sleeve mixes by mixing them with a chemically reactive binder. Sleeves are formed from the sleeve mix and are cured in the presence of a catalyst by the cold-box or no-bake cuing process. The invention also relates to a process for casting metal parts using a casting assembly where the sleeves are a component of the casting assembly. Additionally, the invention relates to the metal parts produced by the casting process.