Sleeping bags, especially down bags, get more and more moisture accuracy,ulation in them every day in truly cold weather camping, especially if weather prevents airing them out. DWR treated down (DownTek and DriDown) do help reduce that retention by about 30% and do dry faster by about 65% but the bags still get damper, colder and heavier every night. Wearing a VBL pants and shirt over a thin polyester or polypropylene base layer kept 90% of that moisture from ever getting into the bag. This keeps the bag warm and light day after day. Most of us may never camp in sub-zero weather (I do) but if you do research VBL clothing. Stephenson Warmlite even sells a suit. And as those who post here know, I am an advocate of 3 mm closed cell neoprene divers' sox over thin poly liners for all cold weather boots, GTX, felt pacs, ski boots, etc. These VBLs keep the boot insulation dry and warm. Eric B.