The visor was hand molded. After the helmet was pep'd and I cut out the visor piece, I cut it into 3 pieces, heated the thermal plastic in the oven on a baking sheet, then quickly took it out of the oven and sort of pulled/pressed it over the pep'd pieces. Same idea as if you were forging a sword; heat up the material, work with it a bit, heat it back up a bit, work with it, etc. And the only reason why we had to heat/work it so much was because it was 1/8" thick plastic (already tinted a dark grey). Then just used a dremel to etch some detailing, then glued it in.
There's a couple other pilot helmets floating around on the forum, but from what I can read on them, they've all been vac-formed then spray tinted.