Abstract: A composite vapor barrier for use between one or more spaces defined by the structural elements (e.g., purlins) of a building is provided. In one embodiment, the composite vapor barrier is formed from a scrim thermally bonded to metallized film and vinyl facing layers. In one embodiment, the scrim can be a triaxial scrim. The composite vapor barrier of the present invention is sufficiently strong such that it does not substantially rupture when a bag of sand having a weight of approximately 400 pounds and a diameter of approximately 30 inches is dropped thereon from a distance of about 42 inches above an upper surface of the barrier.