Abstract: A retrofit method for protecting the contents of a structure having walls and window frames in the walls in the event of a blast outside the structure. The method is effected by (a) providing a flexible and stretchable woven sheet including strands of ballistic thread; (b) attaching a first portion of the flexible and stretchable woven sheet via a flexible adhesive to an inward-facing surface of at least one wall of the structure; and (c) attaching a second portion of the flexible and stretchable woven sheet to at least one window frame in the at least one wall; the flexible and stretchable woven sheet and the flexible adhesive being capable of stretching under impact of the blast, thereby reducing disintegration of the at least one wall and securing the at least one window frame in the wall upon the blast, preventing fragments from the at least one wall and preventing the at least one window frame from being thrown into an interior of the structure by the blast.