The present invention relates to a process for manufacturing a barrier film, wherein the method comprises: —providing an aqueous suspension comprising at least 70 weight-% highly refined cellulose pulp having an SR value of 70-95 and having a content of fibers having a length>0.2 mm of at least 10 million fibers per gram based on dry weight: —forming a wet web; —dewatering and/or drying to form a substrate; —calendering said substrate in at least a first calender nip and a second calender nip; —providing said substrate with at least one first layer of a barrier chemical to form a coated substrate, wherein each first layer has a coat weight of 0.5-5 gsm, and wherein a total coat weight on of the first layers is ≤8 gsm, and—drying to form said barrier film having a thickness of