Every part of your bike has a measure of damping; some parts are better damped than others. Aluminum is poorly damped, steel is damped better, and lead is very well damped.
Lead isn't a practical material for a bicycle; it's soft and it's heavy.
Luckily, it's possible to attain damping that's similar to lead using a technique called
constrained layer damping.
Here's some info on CLD:
http://www.mech.utah.edu/~bamberg/re...astDamper.html
If I had to sum up CLD, it's basically
sandwiching a soft material between two rigid materials. In the doc above, they constrained a soft material (air) with a rigid material (concrete.)
But you don't need concrete; you can do the same thing with glass and aluminum. Airbus does this in their A380 airliner; it's a material they call GLARE (
http://en.wikipedia.org/wiki/GLARE)