Flour may have a similar function as baby powder, which is to serve as an aid to reduce friction but is totally unhelpful in gripping bars.  Flour can be used as an alternative for a lot of things except gym chalk. One can make gym chalk out of flour but it was not proven effective since flour is made up of wheat, which has nothing to do in helping you lift weights, while gym chalk is composed of magnesium carbonate which was designed to dry out the moisture from your palms.