A lot of fans of the Friday The 13th franchise want to know where the idea of the mask came from. So, according to the special effects guy in charge Douglas J White it's quite simple. The mask was supposed to be a generic clear mask that Shelly wore in the beginning of Friday The 13th Part III to scare Andy, however after the director wanted Jason to have a mask with more personality they searched for a better one. As all fans know Jason did not have a mask in Part I (he was in it) and wore a sack over his head in Part II and never got his infamous hockey mask until 2/3 into Part III. So, in Douglas J White's own words here's how it came to be. This is from Crash Army.com
After Stan Winston had sculpted the first head mask for Jason, Steve Miner, the producers and Terry Ballard all brought me an old fashioned hockey mask. This is like the hockey mask Shelly brings with him. The mask looked great but only fit a proper human head. Once I put it on Jason's head it looked rather small. So I had to make a copy of the mask using alginate and poured up a solid dental stone vaccuform buck. There is a technique where you run plastic over the stone form, cut the plastic as if you were making the mask, drill all the holes put the mask back on the stone form and run plastic over it again, take that one of, finish it off and run it again and again until the mask was big enough to fit the head properly. When we finally got the size that Steve liked, I made a new stone form and started making 2 or 3 copies, then painted, added snaps and the red accents.
There you go.