Topband: Support for Flags?

[Eric Rosenberg]

I am about to put up a couple of flag antennas in my back yard (one
running 50 degrees, the other at 330 degrees, with a common support for
the back end). 

I *thought* I needed to use non-conductive masts (I was planning to use
fiberglass masts (from The Mast Company [www.tmastco.com]) as the
supports, but recently heared that I can use aluminum ones without much
(if any) negative effect.  I assume they're lighter and stronger. 

The question, aluminum or fiberglass? 

Thanks in advance, 

Eric W3DQ
Washington, DC