Use duct tape and fill the interior of the helmet. Then using and razor blade cut out the duct tape in triangle patterns (starting at the crown). Then the triangle patterns are your interior pattern. Transfer the pattern to leather or fabric. Give it about a 1/4 of an inch border. Then cut the pattern and sew it up. Use a little cotton or foam padding in the same pattern then glue your new sewn pattern in.
Fantastic looking. I think once you have the link for this cloth, you should put it in the sticky that has other things of this nature. Ya know, the neckbands and gloves and where to buy fan supplies...I cant remember the thread name though.
if you can't find that fabric anywhere else... the same result could really be gotten through making the padding out of 1/4 inch foam, and covering that with any number of swimsuit materials (since they'll be easier on your sweaty head )
that's what i do for the padding inside of any helmet i make.... just cut the pad out of foam, stretch the fabric over, glue, and pin it down till the glue dries. after that it's a simple matter of adding snaps or velcro so that the pieces can be easily removed from your helmet for cleaning purposes.