However, it also has a far higher , so that the moderating efficiency is nearly 80 times higher for heavy water than for light water.

The moderating efficiency gives the ratio of the macroscopic cross sections of scattering, , weighted by divided by that of absorption, : i.e., .

UF is generally chosen over other salts because of the usefulness of the elements without isotope separation, better neutron economy and moderating efficiency, lower vapor pressure and better chemical stability.