The present invention provides a process liner for the preparation of foamed plastic blocks or slabs which exhibits excellent mechanical properties including tear strength, dimensional stability and flexibility while being transparent and allowing easy separation from the produced foam material. The process liner comprising a transparent support polymer film (A) and a transparent peelable polyolefin film (B) provided thereon, wherein the support film (A) has a weight per area of 10-100 g/m2 and is made of a polymer having a melting point of 130° C. or more according to DSC measurement; and wherein the peelable polyolefin film (B) has a weight per area of 10-50 g/m2 and is made of a polyolefin having a melting point lower than the melting point of the polymer of the support film (A) by 10° C. or more. Furthermore, a method for producing the process liner is provided and a process for the preparation of foamed plastic blocks or slabs in a continuous production line.