Gamma radiation is the most penetrating and energetic form of nuclear radiation.
To absorb half the incoming Gamma you need two and a half inches of concrete or almost half an inch of lead. So my eyebrows went up when I saw a press release for an organization called Radiation Shielding Technologies, or RST, selling protective clothing with this startling claim:

"DemronTM not only protects against particle ionizing/nuclear radiation (such as Beta and Alpha), but does what NO OTHER full body radiation protection can do: shield against X-ray and low-energy Gamma emissions."

This sounds like it merits either a Nobel Prize or an Ig Nobel, the award for bad science. Check their site and you’ll find details of an independent test claiming that their anti-radiation blanket really does stop a significant fraction of gamma (about 28 percent at a 90 degree angle).

What’s the secret? Well, the ‘blanket’ involved is 30 inches by 36 and weighs 60 pounds… So it’s basically equal to one-seventh of an inch of lead, and it works because it’s so dense. I checked with RST, and research scientist James Bradshaw agrees:

"You are correct in stating that in attenuation of gamma and x-ray radiation, cross-sectional density is the key parameter. A number of other much more minor effects are also at play, such as the role a supporting matrix has in excepting ejected electrons, etc. We do integrate heavy atomic absorbers into our material, though completely none toxic, that act as the primary attenuation component.
Our material meets or exceeds the absorption capabilities of lead by weight equivalent… Certainly, when it comes to high energy radiation, you can’t beat fundamental physics, but luckily you can get away from using lead."

The point of Demron is not that it has magical properties, but that it is more flexible and wearable than traditional lead-lined garments of the same weight; that blanket they tested might be easier to get over a radiation source than a lead one.
But in spite of RST’s fulsome press releases (including one which imaginatively likened the product to Iron Man’s armor), it’s not going to allow you to walk through heavily irradiated areas with impunity. As with many companies in the defense field, their science is fine but their marketing department may be prone to exaggeration.