Abstract Polymers of tetrafluoroethylene are converted into shaped articles which have a uniform cross-section along one axis, such as ribbons or sheets, which are then processed to produce a fibrillated expanded material. An expanded article or material of this invention is one which has been processed to produce a new article or material of the same uniformity and cross-section shape as the former, but having a lesser specific gravity than it possessed initially. The term ''''expanded'''' as defined herein means lesser specific gravity. In producing the articles of this invention, the fibrillar structures of the molecules within the article are expanded under conditions in which the article is stretched without causing significant decreases in the width or the thickness of the article. In so doing, the specific gravity of the resulting article is substantially and valuably decreased. Less of the material is needed in effecting formations of seals such as used in the formation of pipe joints. The resultant materials are advantageously less slippery and more self-cohesive than the initial material. Further, they are more readily handled and can be used with ease at low temperatures.