Hey fellow SPARTANS,
I had the same problem with my helmet. The Resin is completely hard and I left the helmet longtime outside. But if temperature changed you always had a little resin stink when you wore your helmet. So I nerver could wear it very long (and without risk I guess) so I looked for something easy to use to solve that problem.
And well, I think I found something wich was very easy and it seems that this was even a very effective method. My Helmet doesn't smell to anything now.
Solution is really simple:
You are using finish-color outside your helmet to give it a color. Well just use finish also inside of the helmet. I bought something called "Aqua Lack" (Aqua finish). Its a solid color often used for Children Wood or plastic Toys because it even don't smell in liquid state and it has an enviromental seal because there are no dangerous chemical things in it. So I painted my Helmet inside with that finish (in Black color) and a day later again a second coat from that stuff. I left the helmet outside for about 12-14 hours and today I took it back in and you don't smell anything.
This Aqua based finish is quite expensive (had to pay 5 Euro for 0,125l, thats about $7,75) but I really can recommend that. The resin is now completely covered into a "skin" of finish so no smell can go through. And well, my health is worth every cent, so I really can recommend that investation for those who use resin/fibreglassed helmets.
(Nice side effect is that the "glossy" black painting inside the helmet really looks great in it.
)