Abstract: A thermal insulation structure includes a plurality of inner air and water vapour permeable insulating layers which entrap air and a water vapour permeable, at least substantially air impermeable film layer separating two said water vapour permeable insulating layers, the inner layers being sandwiched between first and second outer air and liquid water impermeable, water vapour permeable outer film layers, the construction and arrangement of the layers being such as to control, in use, water vapour transmission through the thermal insulation structure. Alternatively, a thermal insulation structure includes a plurality of inner air and water vapour permeable insulating layers which entrap air and an inner air and water vapour impermeable film layer separating two said insulating air entrapment layers, the inner layers being sandwiched between first and second outer air, liquid and moisture vapour impermeable outer film layers.