The measured heat flux for the Multilayer insulation (MLI) without fiber Bragg gratings (FBG) sensors and the calculated heat flux from the installed FBG temperature distribution measurement data were found to be coinciding with each other. MLI consists of series of reflecting layers. The heat transfer modes through MLI have complex interactions and also dependent on variety of parameters such as number of layers, layer density, contact pressure and area, boundary temperatures, gas pressure within the insulation, emissivity of the shields, absorption and scattering coefficients of thermal spacers. The theoretical formulation of heat transfer through MLI is subject of many publications. The Bragg grating resonance, which is the center wavelength of back-reflected light from a Bragg grating, depends on the effective index refraction of the core and the periodicity of the grating. FBG sensor arrays with three sensing elements were first integrated on to the test cylinder.