In The Martian, how were the crew in the Hermes shielded from radiation?

Question

I have not read the book of The Martian, but there was one glaring omission in the movie that struck me.

How were the crew in the Hermes protected from radiation?

In space, especially interplanetary space, radiation is a big problem. Look at this from Wired:

A new study highlights one of the big problems with extended space travel: galactic cosmic ray radiation. According to the report, astronauts on the International Space Station would receive doses that exceed their lifetime limits after just 18 months for women and two years for men. A Mars mission crew would be spending at least this long in the harsh radiation of deep space.

The Hermes looks very pretty, but it is all windows and gyms. Not much that would protect from a radiation storm. Even when the crew are discussing doing another round trip, the fact that they are massively increasing their own cancer risk is not mentioned.

Is this covered in the book at all?

Answer 1

It was handwaved.

“In the book they have this really thin, light, flexible material that blocks all radiation,” says Andy Weir, author of the book The Martian on which the film was based. “There’s nothing even remotely like that in the real world. That was the magic I gave him so the story would progress. Otherwise Mark would have different kinds of cancer.”

Answer 2

He would die with that kind of protection.

There were some inaccuracies in the book and the plot. But it was a great book anyway.

That list of doom:

1. Atmosphere

On a reddit Q&A, one fan asked Weir if such withering storms were possible on Mars.

Weir's answer: "No. Mars’s atmosphere is too thin. This was a deliberate concession to drama that I made because it’s a man-versus-nature story and I wanted nature to get the first punch in."

2. Cosmic Rays (Radiaiton Poisoning) (ANSWERING YOU HERE)

After being left alone on Mars, Watney makes his way toward the Schiaparelli crater. Spending that much time on the planet would expose him to a dangerous, and probably fatal, amount of cosmic rays, if not for his handy (and fictional) radiation blocker.

"The book has a completely fictional material that blocks radiation. No such thin, flexible, light radiation shielding exists in the real world" — Andy Weir, author, 'The Martian'

NASA limits its astronauts to between .8 and 1.2 sieverts of lifetime radiation exposure, which would raise the lifetime risk of cancer by 3 percent. Because the sample size of astronauts who have spent a considerable time in space is so small, the exact health effects of cosmic ray exposure is clouded with uncertainty.

The most effective shields against cosmic rays, like water or liquid hydrogen, tend to be heavy and not portable—meaning they’re suitable inside the walls of a space capsule, but impractical in a spacesuit. Researchers are working on plastic cosmic ray shields, but haven’t gotten there yet.

3. Producing Water

Watney mixes hydrazine, a toxic substance usually handled by people in hazmat suits, and oxygen to make drinking water. The admixture also produces ammonia which is poisonous.

“Yes, very toxic. I didn’t know that at the time. Had I known, I would have had him wear his EVA suit during the process,” Weir replied during the Q&A.

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