The simple 2 x 2 twill weave is just one fill yarn over 2 warp, under two, over two and so on, with the warp yarn doing the same. The photo to the right is a microscope image of style 7725 8.5 oz/sq yd fiberglass cloth used in the Rutan type aircraft - though Rutan later changed their style numbers for the 7725 and 7715 to RA5277 and RA5177. This 7725 has and what is now woven and sold as 7725 for use in the Rutan type aircraft has the G75 1/0 yarn in the warp and H25 1/0 yarn in the fill. The thread count published is 54 x 18 ends/inch but it is perfectly balanced, (except of course for the 9 micron G filament in the warp and H 10 micron filament in the fill) so you assume they're counting 3 of the G75 yarn in the warp. 7725 is in effect a visual 18 x 18 twill.