The primary functions of Polyester forming fabrics are to permit water removed from the sheet to flow through the fabric support retain and form the sheet and to convey the sheet from the head box to the press section.The top surface of the forming fabric acts as a filter cloth to create a base for fibers to be deposited to form a fiber mat.   
The Polyester forming fabrics paly an important role in paper making process.A sheet of paper begins in the forming section, where a mixture of 99% water and 1% fiber is introduced evenly across a forming fabric, which acts as both a sheet conveyor and a dewatering device. It is here that the paper sheet is formed and the initial water removal occurs. 

Today, Polyester forming fabrics have an average operating life of 45 to 60 days.(Even More than this which is depending on the usage and many more machine parameters.)