Well lately, i have made my noble six helmet fit my head. (WOOOOOOOOO!) And i will soon be hardening it. Now my confusion is to what i do. I hear about resin, fibreglass, bondo, rondo and all this and im not sure what im supposed to use.
BenStreeper has some very good tutorials on the different methods, but it really depends on what application the helmet will be used in.
If you're going to wear it: I highly recommend a minimum of 2 coats of resin on the outside, fiberglass the inside, followed by the bondo/finishing stage on the outside. Some people also use rondo for that stage in place of bondo, due to the fact that it can be brushed on.
If you're going to mold & cast/display it: Follow all of the same procedures on the outside, but fiberglass would not be necessary on the inside. In place of that, you can use rondo to slush cast it to harden it. Again, Ben has a spot-on tutorial for that.
To explain some of the terms, in case you aren't sure:
Bondo is the name brand of a 2-part polyester body filler available here in the U.S. When looking for them abroad, just look for something similar.
Rondo is a term used to describe a mixed solution of body filler and fiberglass resin, combined in a certain ratio to fit each application, with hardener mixed in of course.
Just keep in mind, that if you still have questions, don't hesitate to ask. We're all here to help.

I hope that helps.
-Matt
p.s. - my surname is very Irish by the way.