Abstract: A polyester filament nonwoven ply is suitable for roofing and roof-sealing webs and has a latent shrinkage force which counteracts drafting forces which may subsequently occur as the result of stresses or during thermal processing operations. The roofing webs thus remain dimensionally stable even when exposed to heat. The shrinkage force is obtained according to the claimed process by drafting the ply accordingly in a drafting mechanism arranged after a dryer.