I used a heatsheet under my hammock and a thermarest trail in-between my dual layer BB on the 1st annual Florida hang about a week ago. I was completely warm and cozy with the temperature getting down to 26 degrees. I got a couple of snickers from a few people about my makeshift underquilt, but some of those same people were packing up around midnight from the cold. I was thinking about sewing a heatsheet into the bottom of the underquilt I'm making, hope to make a sub-0 degree underquilt using only 12oz of down. Thanks for turning me on to this!