I tried a clear pla filament from http://diamondage.co.nzdiamondage.co.nz though the following might apply to other manufacturers as well. When I print only 2 horizontal layers can get very close to transparent if the speed is slow and extruder feed is calibrated correctly. However if I try same 2 layers vertically result is opaque. So if you want a flat visor it might be possible. Probably easier to make a shaped mould with printer then find some old plastic packaging that is heat shapeable at lower temperature and then stretch it over the printed mould. Not elegant solution but should work.