Originally Posted by
staehpj1
I have not had a problem keeping my down bag dry enough even when using a bivy. Sometimes there would be a bit of water or ice on the surface, but it brushed right off (the bag has a DWR shell). I don't think I'll buy another synthetic bag unless the technology improves significantly. I do have a nice synthetic bag that I use when camping with my daughter because she is quite allergic to down. If sleeping in the same tent as someone in a down bag she wakes up with her face all puffy and sinuses all stopped up. My synthetic bag is a 20 F North Face Cat's Meow and is a lot warmer than I typically need.
In warm months it's easy to keep a bag dry. You night get some condensation in your tent/bivy that then drips onto the outside of your bag, but the down itself will stay dry. The danger comes when it's cold, then your sweat can actually condense inside the down. This is why some people recommend using a vapor barrier inside the bag to stop water evaporating form your body ever getting to the bag. You'll stay warm, but it sounds very uncomforatble to me.