Protecting astronauts from deep-space radiation is a major unsolved problem. Consider a manned mission to Mars: The round-trip could last as long as 30 months, and would require leaving the protective bubble of Earth's magnetic field. Some scientists believe that materials such as aluminum, which provide adequate shielding in Earth orbit or for short trips to the Moon, would be inadequate for the trip to Mars.

What material seems to be an appealing alternative according to NASA?

Water. (source)

They also discuss generating electrostatic fields onboard the spacecraft or using cryogenic liquids such as liquid hydrogen or liquid nitrogen, though they present hazards of their own.

quote:

The atoms of liquid hydrogen are particularly good as a screen for galactic cosmic rays because they don't fragment into secondary particles as much as heavier elements -- like lead -- do when bombarded by high-energy radiation.

Interesting topic, Mozart. Thanks.

Interesting,Professor, especially if astronauts have to walk on Mars ,their suits have to be protected as well.
But my question was about the material "the spaceship itself" would be made of.

I, too, was talking about the spaceship itself. According to the article, "Spacecraft designers may also use a ship's own cryogenic fluids as a radiation screen by arranging the cargo tanks containing them around crew compartments." I figured the same goes for water tanks as well.

Is the answer you're looking for a solid material of some sort?

Yes, solid material. I am sure there is a possibility that water could be involved somehow but my source doesn't mention it. It is relatively new (8-25-05 article) discovery.

Hint: this is a material that we all use and touch every day but has been
"transformed" by NASA.

I have read about hydrogen storage in graphite being an excellent shielding.

Plastic, to be specific, RXF1, which is based on polyethylene, a common plastic used to make garbage bags and other low-tech items.

Sailracer found it.

Plastic Spaceships

Is there any truth to the rumor that the UK ships will use some of Karrow's recipes to produce an impenetrable shield?