Over the weekend I had good results using a vapor barrier (bread bags in my case) in warmer weather (low 30s and up), at least until one of them developed a hole. However, I was just reviewing their proper use online, and I see that it's recommended to use VBLs under your socks whereas I was using them over my socks. My thinking was that, yes, I was going to have wet feet from perspiration, but at least it would be warm wet feet. On the other hand, without the VBL, or with the VBL under my insulation, the cold water from the marsh I was hiking through would carry away all the heat very quickly, and I'd be left with wet and cold feet. It seems to have worked out for me the way I imagined, but perhaps it's different in colder weather? Maybe whoever came up with the VBL concept didn't really intend for them to be used in a wet environment with light shoes? Does anyone have any thoughts to add on this based on theoretical or practical experience?