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!

at what nightly temperature will a sleeping bag exposed to open air be unlikely to collect condensation?

The dew point is a combination of both temperature and relative humidity. If you go to the wikipedia article on "dew point", you'll find an explanantion and a table of temps vis a vis humidity that will give you a rough idea of how it all works.

The main thing to know is that warm air can hold more moisture than cool air, so as the air cools at night, it will eventually cross a line where it can't hold that much moisture any more, so it condenses and falls as dew. When it crosses that line depends on how much moisture there is in the air to begin with.

Thanks! Perfect!

http://forecast.weather.gov/MapClick.php...p;FcstType=text

This is the National Weather Service website. Lets assume you live in Navato. You click on the map until you get the page shown above. At the bottom of this page there is an option called "Tablular Forecast". Click on that and you will get an hour-by-hour forecast for the dew point.