Lugana 25 Easy Count (EZ Count or Easy Grid) white fabric. 52% cotton, 48% rayon, 55” wide, 25 stitch count. Zweigart
The gray grid marks every 10th thread. The grid will wash out with warm water (test first before stitching), but this fabric is especially nice for full coverage stitching so you don't have to be concerned about the grid washing out. Normally Zweigart recommends 40°C (104F) and 40 minutes in the washing machine. And when there is still some grid, to wash it again. Important is that it is washed in the washing machine and not by hand.
Zweigart Aidas and Luganas can also be washed with 60°C (140F).