A flexible heat barrier is configured to absorb and deflect heat energy and utilizes a multilayer construction wherein each layer provides a specific purpose. An outer layer configured for exposure to a heat flux includes a coating having an intumescent component and an opacifier component. An inner layer includes a foil that may include a high emittance coating to more effectively reflect radiation. A middle layer includes an insulating fabric layer that may include oriented fibers that can effectively polarize radiation and may include a plurality of layers of oriented fibers that are configured at an offset angle to deflect and reduce radiation transmission through the middle layer. A flexible heat barrier may also include a flexible gas barrier that includes a phase change material, such as frits that melt at a predetermined temperature and flow into gaps to reduce the permeability and further block heat flux.