Kokoda - underwear

Hi,

I am doing kokoda next month, and starting to get fairly excited about it... nervous as well (back injury - but thats a whole other story)... anyway I have a question about Underwear over there.

I have a pair of Bike Shorts to wear under my shorts, but I don't feel entirely comfortable "freeballing" in them, and worry about chaffing... therefore What material underwear do you recommend I wear underneath them?

I want to avoid cotton (for obvious reasons), is nylon or lycra any better?

What have other people done in the past???

Thanking you in anticipation.

Michael.

Oh and thanks for sharing the details of your intimates... lol