Titanium
Titanium is most known for it's corrosion resistance and strength to density ratio, the highest of any metallic element. It's half the weight of steel for the same tensile strength and twice as strong as aluminum alloy. In practical terms this means we can use less material (ie. thinner tubing) to achieve the same strength. Combining this with it's ductility means we can create incredibly light frames, but still maintain incredible compliance and ride feel.
Titanium is also much more resistant to fatigue and impact than aluminum alloys, and it's natural protective layer of Titanium Dioxide shields it from the elements.
A perfect balance between carbon fibre, aluminium and steel.