I came across a question on Google the other day asking to define the word scrim. Scrim is basically the grid-like reinforcement used in most of the PVC roofing membranes that we use on a regular basis on flat and low sloping roofs. In PVC multiple scrims are used and the "thread count" can depend on the thickness of the membrane used. We normally use 45 mil, 60 mil, and 80 mil PVC membranes from 2001 Company Inc or Duro-Last. That way our customers can choose between the different thicknesses and warranties according to what their price range might be, 80 mil being the thickest with a 25 year warranty. Though PVC is just one of the many options we carry for flat and low slope roofs, it seems to be the most popular in our business right now.
In the picture the strength of the scrim can be seen in the 80 mil PVC.