I thought protective jackets were designed for motorcross only but I'm now seeing many advertised for track. There are all sort of models, some of them will make you look like a middle-age iron cast warrior. Here's a couple:
http://www.revzilla.com/motorcycle/dainese-wave-pro-jacket
http://www.revzilla.com/motorcycle/icon-field-armor-stryker-vest?gclid=CLbn-LTyoLsCFbB9Ogod9RMAPA
Anybody has experience with these? Is there any value compared to a simple back protector?