Go to your local pickapart junkyard, find a rear vent panel or two (you know, the battery cover on the pass. side, or air filter cover on the driver side) Depending on the year and model you pick, the backs of them are lined with honeycomb shaped material, Your car might have them-check it out! After I found this out, I picked up a couple from the junkyard, I'm going to make screened grilles for the front of it!
------------------
'86 SE V-6 (Soon to be V-8, I hope!)
'75 Fiat 124 Spider
'88 Ford T-Bird Turbo