Okay... I slept in my backyard last night, trying out a sleeping bag (Mountain Hardware Lamina 20). The forecast was clear, so I didn't bother with a tent. The temperature dropped to 39F.

I woke at 3AM and felt the outside of the bag. While the inside was dry, the outside was extremely wet. I nearly called off the experiment, but I was warm enough and wanted to see how I would fair in similar circumstances outdoors.

At 7AM ducks landed near my head and wouldn't stop quacking. I also dreamed that a cat crawled into my bag and the air mattress punctured. Apparently it was time to get up. By this time the outside of the bag was soaked. The inside was still warm and dry.

So here's my question... at what nightly temperature will a sleeping bag exposed to open air be unlikely to collect condensation?

PS: For reference, I live 10 miles from the Pacific coast.

Thanks!