Reading about the Kirk magnesium frame on another thread, which is a truss/beamed frame and thinking of folding bike design has me wondering if fabrication cost is the reason that tubes are overwhelmingly chosen as material for bike frames. Does anyone make, say, titanium frames out of girder like material?

I chose titanium because it would seem (in my mind at least) well suited for that kind of a design and I'm pretty much convinced that aluminu is an unacceptabe material for the higher stresses of a folding bike.

TIA for any reply,
DG1