[quote author=Tim Wescott ...as far as I know, no one makes a material that is suitable for this sort of thing that is also flexible. Is there anything that you can put into a highly-curved layup, like a cowl, that would do this job? Clearly it would have to be something that's flexible during layup, but which cures out rigid -- I'm envisioning a cloth made out of lightweight fibers, or tubes, or miniature foam spaghetti, or something else that will wet out with the epoxy and cure into something rigid, but which wouldn't lend much mass for its bulk.
The only other alternatives that I know of for a cowl or other similar structure would be to mold or otherwise form the inner portion (expensive), use lots of layers in the layup (heavy), or leave all that out and have yourself a flexible cowling.
So, is there an answer here? Or do you just make a flexible cowling and live with it?
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Old thread but anyway;
There is a material you describe, it's called Coremat. With quick search the thinnest available seems to be 1,4mm.
But I'm not convinced that that is a good product for small parts like cowlings.
At least Rohacell sheet can be heat formed before molding but with tight double-curves like in cowling, you propably have to make it from several smaller pieces.
I'd say the best way is to pre-form wet light balsa (0,8..1mm) over a plug or in mold and once dry, suck it in mold between 2 thin glass cloths.
That's how Yatsenko's do it.
Also, thin honeycomb is very flexible.
L