Materials for ducting / fan adapter?

[stultus]

For some odd reason my 80mm L1A Panaflo on the hand-made fan adapter I bought still whines. The fan does not whine when it is off the adapter. So, that means (to me) that there's airflow resistance/whatnot that's causing it to whine. I want to make my own adapter. (That's just my luck. The "quietest" fan in my system is making the most noise. Other two fans are the fan on my GTS and the fan in my Whisper PSU.)

What material are they made out of? What should I buy at the hardware store? Is there a FAQ on this at all?

 

[Cosmo3]

I made a fan adapter from a pice of Aluminum drier vent pipe and it worked out fine. I made a 92mm fan adapter to use on my toisol cpu heatsink. I like the aluminum because you can cut it with sissors so it is easy to work with. I think my cost was less than $2 for the pipe.