Flexon spectacles, c 1990s.
© Science Museum / Science & Society Picture Library
Flexon is a metal alloy of titanium and nickel. It was developed by US Naval Ordinance Laboratories and used in jet aircraft, NASA research projects, super computer electronic connectors and a few experimental medical products. Its defining feature is that it can 'remember' and return to its original shape after bending and twisting. It is eight times springier that spring steel, 25 per cent lighter than conventional metals and corrosion and fatigue resistant. Its properties made it ideal for use in spectacle frames.