Sleeping bag liners for camping? My friend Dion made fun of my "poor excuse for a sleeping bag," but it kept me warm as the temperature dropped to the low forties, and it weighed only five ounces. We were camping on the banks of the Manistee River in Michigan.
So, how did it a sleeping bag liner keep me warm? The real secret was the fifteen minutes we spent gathering dead, dry bracken ferns to build a two-foot thick mattress. We set the tent on that. Then, in my liner with all my clothes on, I was fine. Actually, I've rarely slept as well camping as I did that night.
Using Sleeping Bag Liners Instead Of Bags
You can buy light sleeping bag liners from Campmor and other suppliers, or do like I did. I sewed a simple one of bargain-bin nylon material ($1/yard) obtained at Walmart. Buy the lightest nylon or polyester material you can find. Depending on what you use and how big you make it, it should weigh between four and nine ounces.
I found I could stay warm with a light sleeping bag liner in autumn, at a few degrees above freezing, so this strategy should work well for summer nights in the sixties. Be careful, of course. It could be dangerous, or at least uncomfortable enough to ruin your trip. Test this strategy near home, and know yourself and your enviroment.
You may want to learn a few tricks for staying warm if you try this strategy. When it isn't too humid you can breath in your bag, for example. Many backpackers will tell you not to do this, because you'll be damp in the morning, but in a dry enviroment you'll dry quickly once you hit the trail. Spread the liner out to dry during a break.
Just as I did the first time, you can also use a mattress of dried plants. Use dead leaves, palm fronds, grass, cattail leaves, some softer tree barks, etc. A mattress of this sort insulates you from the ground, which normally takes away much of your body heat. Scatter the leaves in the morning so they won't smother the plants underneath.
Try to go to bed warm. If you're warm when you get into your sleeping bag, you're more likely to stay warm through the night. If you start out shivering, it's difficult to warm up, especially in a thin bag.
More tricks for staying warm: Hot tea before going to sleep... Exercise a bit... Cover yourself with extra clothes... Elevate your feet slightly... Go to sleep earlier or later. Experiment to see what works best for you.
These are options, but not recommendations. I've gone out with nothing more than a bivy sack in my jacket pocket, but I'm not recommending that either. This is just to present all the possible options for the ultralight backpacker. One of those options is sleeping bag liners.