my design wall is 96"x96" - insulation board mounted directly to the wall - gridded flannel affixed to the insulation board with a slightly diluted Elmer's Glue type thing (so as not to "eat" the foam insulation). Yes, there is a seam down the center but I stitched it perfectly. The gridded lines help with placement of blocks when I am rearranging blocks - I don't have to reposition the first layout blocks nearly as much as I did without the lines.