Practically it really hasn't. Polyethylene is being tested in NASA's Radiation Shielding Program but I don't believe it's been put into service for a manned mis

Practically it really hasn't. Polyethylene is being tested in NASA's Radiation Shielding Program but I don't believe it's been put into service for a manned mission. There are also tests being conducted with adjustable "magnetic bubbles" that can in theory shield a spacecraft from radiation, but the last I heard they were done on a much smaller scale and would require a huge amount of power. NASA has been making progress in making astronauts less susceptible to radiation damage through diet and vitamins. There's also this paper which talks about a vaccine that's being tested to counteract some of the body's responses to radiation exposure (PDF): http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20070021485_2007019108.pdf http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/2007002...