From the GMA Techline
Subject: Warp and fill — What do the terms warp and fill mean with regard to tear strength of a polypropylene liner? (Michael, Alaska)
Reply: You ask a fair question that has a simple and difficult answer to it.
The simple one is that the polypropylene membrane you are using is scrim-reinforced (manufacturers sometime call it “supported”). Its proper designation is fPP-R. This scrim is an open woven fabric and has intersecting yarns in the machine direction (the “warp” direction) and the cross machine direction (the “fill or “weft” direction).
The difficult part is that I have to assume that the scrim is a 10×10 fabric meaning 10 yarns per inch in both directions. This is the most common type of scrim used for fPP-R geomembranes. If this is the case, then the tear strength is about equal in both directions. It will take a little more deformation in the warp direction for the strength to fully mobilize, but the strength values will be about the same at break.