A monolithic metal thermal insulating sleeve liner for fluid flow devices such as valves and piping used in severe industrial applications is additively manufactured (e.g., by 3D printing) to fit the bore of a protected fluid flow device. Tessellated support structures obliquely extending between inside surfaces of inner and outer shells provide increased resistance to thermal conduction while also providing increased strength against compression forces. Example support structures include an array of four obliquely oriented elongated members mutually intersecting mid-way between the inside surfaces of inner and outer cylindrical shells. If internal interstices are sealed they can be vacuumed or pressurized to enhance thermal insulating properties. A pressure equalizing aperture can be provided on or through the sleeve if needed in some applications.