srw
It's a bit more complicated than that...
Or just don't bother with a helmet....If you need to be a bit careful of your hair (assuming people who wear heels have worked hard on their appearance, including their hair) check out the helmet http://www.hovding.se/ Until this post, I had not gone back to see if this idea was launched. But, I guess they are available. Cool but expensive.
(See the helmet thread for the latest discussion on the Hovding. An expensive fashion accessory and an unsuccessful business would be my short summary.)