hey big...check out vectorply....
http://www.vectorply.com/reinforcemt/search2.aspx
If you search E glass for 0 and 45 degree double bias with mat, you get 1708.......0 and 90 degree double bias with mat you get 1808....all their glass is stiched rather than using a binder so it seem the use the number to refer to the fiber alignment. Not sure if every manufacturer does the same.