when finishing a helmet what type of coat to seal it?

when finishing a helmet what type of coat should i use to seal it matte? clear? idk im using rattlecans

i would use Testor's Dullcoat...expensive, but the stuff rocks!! =) probably need at least 2 cans...

I used a matte clearcoat as wel, but something cheap. I bet what FettDad recommended will do the job in the best possible way.

def gonna try it on a test peace thanks guys