I was thinking about this as I slept in my bag a few nights ago. Assuming most folks do not sleep on their side the entire night, the bottom of the bag is really a waste. The down or other filling on the bottom seems to be doing little. It seems to me the biggest need of the bottom is to keep the ground from sucking your heat out so maybe we should have the sides and top nice and fluffy with down but the bottom maybe inflatable air pockets or a super lightweight but dense pad to keep you off the cold ground.

Yes, its the loft that traps our body heat that keeps us warm. The stuffing underneath doesn't do much. Thats where a good pad or pads come in. Look into "Big Agnes" sleeping bags. They are made with nothing on the bottom but a sleeve for your pad (so you don't roll off it)......

As mentioned, Big Agnes and others have systems with pads in the bottom and insulation on top.

I think it's TNF's Blue Kazoo that has synthetic on the bottom and down on top - synthetic compresses less under your weight.

Top-end bags like Western Mountaineering have baffles which wrap all the way around the bag. You can then slide all or most of the down to the top when it's colder out, and put more on the bottom when it's warmer.

Quilts and bags without down on the bottom or eliminating the underside all together has been used by ultralight backpackers for awhile. You can cut a lot of weight with this type of sleep system.

http://www.gossamergear.com/cgi-bin/gos ... light.html
http://www.nunatakusa.com/

You guys still stuck on sleeping bags! Come on, the future us here!

Back in the 1970s, Western Mountaineering used to make sleeping bags without down insulation on the bottom. Instead, they had a sleeping pad on the bottom.

They are no longer making sleeping bags in that manner. Says something about their success with that design?

Well, thier current continuous baffle design is just way more versatile. You can buy a lighter bag and shift the down to the top if you wish. There's no pad sleeve, but I neve have a problem staying on my skinny NeoAir anyway.

I have the Big Agnes Lost Ranger. In cold weather, I found I needed a good insulated pad -- or sleep fully clothed -- I lost a lot of heat with the Big Agnes 2" air pad.

butitsadryheat wrote:My brother had been doingit for years, and finally talked me into sleeping with just the pad underneath, and using the bag more as a blanket.

What a difference. I am a side sleeper and spread out a bunch, so mummy bags are often uncomfortable for me, but this last trip. Wow. Haven't slept that comfortable in awhile.

Wait, that just sounds totally ridicules, stop telling us stories!

I think I'll try that this summer. In the winter, I don't see how that could work as well.

I have a bag that has no bottom insulation that I use for summer. It saves a lot of weight, but because I'm a side sleeper it is not the most comfortable bag to sleep in.