See http://www.fieldscorp.com/products/prodInfo/burG362_62pi.htm...
for the following text:
"An open weave fabric that has 20 threads per inch in the warp direction (length), and 10 double threads in the fill direction (crosswise). In industrial applications, the 20 x 10 weave is preferred because the mesh openings are larger which gives the bitumen a better chance to key through the openings to form the important bond. This light weight, high tensile strength, bi-directional fabric will not rot, char, tear, or wear."