Looking for some clarification as to what exactly separation fabric does, how it does it and why. Simple right! I understand the basic principles of what the fabric does, preventing migration and shifting of the base materials and I think I have a general grasp of how it does this but... The last patio that I put in (just last week) I decided to go all in and bought a roll of Mirafi 500X separation fabric from my paver dealer. A gigantic 5400 square foot roll that weighed 210 pounds. This stuff looked very similar to the Lumite product (http://lumiteinc.com/Product Lines.html) that i had been using on my previous patios when needed. The only differences that I can really see are, the Mirafi product feels a bit heavier, but not by much. The big advantage to the Lumite product - it comes in much more manageable rolls. It is sold as a weed barrier/ground cover product and comes in rolls from 3' to 20' wide. Is there a structural difference between these products that makes the Lumite unacceptable, or do they just choose not to market the product in the same way Tencate does?