Abstract: Bladder insulation which is adapted to be inserted within the wall cavities of existing buildings is disclosed which provides for high quality insulation having a high R value. The invention describes a bladder or impervious bag constructed of two thermoplastic sheets of material hermetically sealed at both ends and on each of the sides. The preferred film used herein is urethane although polyethylene of from 4 to 15 mils in thickness may be employed on the inside and/or the outside of the bladder. This bag can be inflated within the wall cavity and filled with various insulative materials and/or pressurized with various fluorinated hydrocarbon gases. The various insulative fill materials used may be, but to be all not inclusive, vermiculite, mineral wool, microballoons of either glass or plastic, and eggcrates, or any combinations of these materials.