The attenuation factor depends on the density of the material used for screening thus, referring to the precedent example, the halving thickness of concrete as compared to packed earth will be 2.4 inches (6.1 cm). The protection factor is increased by multiples of two, i.e., 2, 4, 8, 16... 1024, 2048... and so on which means that the intensity of the incoming radiation is halved with every interposed halving thickness.

Fallout protection is relatively easy to achieve. Any material reduces the radiation intensity in proportion to its density, therefore the heaviest the material the more effective the shielding and the greater its thickness the greater the reduction. The thickness of several common materials needed to reduce the nuclear gamma radiation by a factor of 10 is shown on the table on the left. The amount of reduction between the surface receiving the radiation and the opposite surface of the halving material is called protection factor (PF) , hence the thickness of each material in the list will provide a protection factor of 10.
Additional protection may be added to an average home basement (below, left) with a protection factor of 10, where a family sheltered in the basement would still be exposed to dangerous radiation levels. Typically, after 7 days an accumulated dose of about 400 rems would occur inside the basement assuming a totaled outside radiation of 4,000 roentgens. An additional piling of 18 inches of dirt against windows and exposed walls before the fallout starts would attenuate it to about 40 rems while 36 inches of dirt would reduce the dose to 4 rems.

Local fallout zones will inflict small doses of radiation on the people who are on the fringe of fallout zones, or on people who are in fallout shelters in zones of heavier fallout. Even the best fallout shelter attenuates fallout rather than completely blocking it, and fallout shelters simply insure that people who would receive lethal doses will instead receive sublethal doses which, however, may still produce long-term effects for some percentage of those exposed.