NASA Testing New Class of Fuel-tank

It is no mystery that the traditional  material for NASA's high pressure cryo-fuel tanks is metal of one type or another.  Metal pressure vessels and fuel tanks are good at what they are designed to do, however the down side is that they invariably have a large weight penalty.

So with this in mind NASA  has begun testing fuel tanks that are made of composite materials.  The aim of course is to significantly reduce the weight of the launch vehicle or other parts of the mission.  Less weight equates to lower costs and larger payloads.  

To use composite fuel tanks, a number of breakthroughs in manufacturing needed to take place. A breakthrough in automated fiber placement which will help eliminate leaks and tooling that will eliminate the heavy bolted joints, which composites perform badly at. 

Below is a NASA film describing the process of manufacture and the ultimate weight savings.