A water vapor permeable multi-layer thermal insulation (10) includes two water vapor permeable outer layers (16, 18) encapsulating inner air and water vapor permeable layers (14) of insulation material and at least one inner separating layer (12) of an air-open fibrous material interleaved with the inner thermal insulation layers (14) and having a mean flow pore size that allows water vapor to move from one side of the at least one inner fibrous separating layer to the other and through the inner insulation layers yet restricts mass movement of air from one side to the other of the at least one inner fibrous separating layer (12) to form a barrier to convection.