A method of occluding a defect in the wall of a body vessel is provided. An outlet portion of a microcatheter is delivered to the defect, then at least a body portion of a thin film occlusion device is radially expanded from a collapsed orientation to a deployed orientation for engaging the microcatheter and covering at least a portion of the defect. Thereafter, an embolic media is released into the defect from the microcatheter for facilitating thrombosis. The body portion of the occlusion device is substantially porous in the collapsed orientation, but substantially non-porous in the deployed orientation for preventing prolapse of the embolic media into the body vessel.