in the US, the raw glass (sheet) that makes up the windshield is ~ the same as far as strength; there are only a few companies that actually make raw glass because it is a VERY expensive proposition. PPG does make raw glass. Ford had one of the biggest glass plants in the US but that has been spun off and dunno who owns it now or who they supply. Thicker windshield glass (2.0 mm is standard, 2.3 is also used) is actually cheaper than 2.0 because it has a higher yield in production- less scrap loss. Most mfgs use 2.0/2.0 glass because it's lighter and defrosts quicker. Some use 2.3/2.0 for cost savings- the 2.3 is the outside sheet, 2.0 inside. The major difference between OE glass and aftermarket is cosmetic quality- edge chips, scratches, etc, and not strength; some rejected OE glass goes into the aftermarket supply.