Style 1800 fiberglass cloth is a 9.8 oz/sq yd plain weave boat and tooling type fabric with a thread count of 16 x 14 ends/inch. Style 1800 uses the yarn ECK 18 1/0 in the warp and fill. The "K" glass filament is 13 microns and is much bigger than the 9 micron "G" filament used in style 7500 fiberglass cloth that has the same weight and thread count. The thicker 13 micron filament flatter yarn in 1800 makes it quite a bit stiffer than the similar style 7500. Style 1800 here is finished in pure Volan and will have a green tint. Because it is a much cheaper and stiffer fabric than the style 7500 it is priced lower.