Astronauts on future long-duration missions will be exposed to different kinds of ionizing radiations, Earth's plasmashpere and Van Allens radiation belts, solar flares and galactic cosmic rays. What are the cutting edge materials which could be applied for radiation shielding? 

Is there some universal material which could be used for all types of radiations or there should be a layered protection, each layer dedicated to specific type of radiation? 

Also what would be the minimal thickness of such protection which can confidently guarantee (NASA 95% confidence level) that astronauts will receive less than 50mVs during the flight to Mars?