Articles made of a porous material having a fibrillar microstructure of bent fibrils and provided with a fracturable coating whereby the physical size of the article may be changed by the application of force to the article in a direction substantially parallel to a direction of orientation of the fibrils. The application of a tensile force to such an article in a direction substantially parallel to orientation of the bent fibrils results in fracturing of the fracturable material and straightening of the bent fibrils. Methods of making such articles are also described. The articles may include implantable articles such as vascular grafts and stent-grafts； such devices may, for example, be forcibly increased in diameter or in length wherein the force results in fracturing of the coating. One such coated material is porous expanded polytetrafluoroethylene provided with a coating of fluorinated ethylene propylene.
