http://www.greenbaypressgazette.com/...dell/86820896/

Hornung admits to wearing a leather helmet in college, plastic Riddell as a pro. Claims Riddell knew enough way back then to have warned him.

This seems like a hard one to prove. Seems like Riddell can argue they were a vast improvement over what he wore in college, and were probably at the leading edge of the technology at the time.