I've slept in a waterproof/non-breathable hammock before (Crazy Crib) and didn't have any condensation problems. Surprised me, but I didn't. Temps were between 30s and 80s.
Gardenville made a cuben hammock and I don't remember him posting any bad results on condensation. He also made a cuben TQ, though...maybe he just didn't post about it b/c he was going for a VB effect.
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