Go to this link...
http://405th.com/forums/index.php?showtopic=18292 Thermorform is making a male mold, that won'd bond to your visor. It needs to be SLIGHTLY smaller than an original, to account for plastic thickness. Basically, you heat your plastic (only certain types work) and pull it over the maser. Google for more info. Vac-forming is the same, but it works better. Also costs more...