This is the Iron Man Mark 46 Helmet from the Captain America Civil War movie.
I have not printed this helmet out yet but, I think if printed at 100 -105% it should fit an adult head. Check pdf file for dimensions. Units are in mm. If you do print this before I do, please let me know what scale fit your head.
I design props and costumes mostly. I am not an engineer nor a trained artist. I learned almost everything from watching Youtube videos and just messing around in designing software. I started designing with Fusion 360 in August 2016.