Matt it doesn't matter.
It only matters on materials like Tufnol that have a 'grain' Oilon is an extruded plastic so bar or sheet will be the same.
With Tufnol you always have to use sheet and not bar [ or rod as they call it ] as the rod is laid up by wrapping and for a gear it will break a tooth off very easily.
Gears need to be made from Whale brand cloth woven which is the best brand for this purpose.