Two applications of rubber coated fabrics in energy extraction are described in this paper. The first is in wave energy where the use of a rubber membrane air bag as the primary interface to the waves leads to a highly efficient device with a good bandwidth. The second is in low head hydro-electric devices where a membrane serves to separate the water from an air chamber which is linked to an air turbine. A form of 2 ply cross corded construction for these membranes is described, with the angle between the cords dictating anistropy in the elastic and strength properties of the bag. By judicious choice of this angle the differing orthogonal requirements of a membrane can be satisfied. The membrane material will be constructed from 2 plies of nylon cords coated with a natural rubber/polybutadiene rubber blend (NR/PBR), to a total thickness of 4 to 5 mm.