  The gas SF$_6$ has become of interest as a negative ion drift gas for use in
directional dark matter searches. However, as for other targets in such
searches, it is important that radon contamination can be removed as this
provides a source of unwanted background events. In this work we demonstrate
for the first time filtration of radon from SF$_6$ gas by using a molecular
sieve. Four types of sieves from Sigma-Aldrich were investigated, namely
3{\AA}, 4{\AA}, 5{\AA} and 13X. A manufactured radon source was used for the
tests. This was attached to a closed loop system in which gas was flowed
through the filters and a specially adapted Durridge RAD7 radon detector. In
these measurements, it was found that only the 5{\AA} type was able to
significantly reduce the radon concentration without absorbing the SF$_6$ gas.
The sieve was able to reduce the initial radon concentration of 3875 $\pm$ 13
Bqm$^{-3}$ in SF$_6$ gas by 87% when cooled with dry ice. The ability of the
cooled 5{\AA} molecular sieve filter to significantly reduce radon
concentration from SF$_6$ provides a promising foundation for the construction
of a radon filtration setup for future ultra-sensitive SF$_6$ gas rare-event
physics experiments.
