A sleeping bag liner serves as an insulating layer inside a sleeping bag, it provides a layer of protection between your body and any water bottles or clothes you include in your sleeping bag at night and they keep your sleeping bag clean from dirt and body oils. A sleeping bag liner might consist of a fleece blanket, silk mummy bag or a vapor barrier bag. My experience is that blankets tend to get tangled so look for something shaped like your sleeping bag.
I routinely use a silk sleeping bag liner inside all my sleeping bags for both comfort and warmth.
- A sleeping bag liner adds warmth. It can add several degrees of warmth to your bag depending on the fabric, which allows one to buy a lighter bag but still get the temperature rating of a heavier bag.
- For individuals with old sleeping bags with compressed insulation that has lost warmth, a liner allows a boost to the warmth and delay the purchase of a new bag.
- A liner can act as a draft barrier keeping users warmer and can fill up the excess room in a mummy or rectangular bag, boosting warmth.
- A liner keeps a sleeping bag clean and minimizes the need for laundering. Washing a liner after a trip is way easier (and cheaper) than going to a Laundromat and washing a whole sleeping bag in a large commercial machine. Washing a sleeping bag is the fastest way to ruin it. Most manufacturers recommend using a liner and just spot-cleaning the sleeping bag.
- A liner adds comfort. A liner made of Silk or CoolMax is more comfortable against the skin than the linings of many bags.
- Many liners will help wick away moisture, keeping users drier to help them sleep more comfortably. And a liner helps avoid the initial shock of climbing into a cold sleeping bag.
I have used a DesignSalt silk sleeping bag liner for 5 years. I have used this liner in a variety of weather conditions with temperatures ranging from -teens to mid-70s. The silk liner is lightweight – it only weighs 4.7 ounces. The liner adds 9.5 degrees of warmth to my sleeping system. It is breathable, wicks moisture away from skin and is soft and comfortable to the skin. Finally it is the ideal size. I am 6′4″ and found the sizing of liner to be ideal. The 95″ long bag features a drawstring hood, a 35″ wide opening taping to a comfortable 22″ boxed foot end.
A vapor barrier is made of a waterproof, non-breathable coated material and the concept is to keep a sleeping bag dry on multi-day trips by preventing body perspiration from getting trapped in the insulation of the sleeping bag. In ideal dry conditions the heat generated by the body drives the moisture through the insulation. However, in extreme cold this moisture might become trapped in the insulation and freeze. By using a vapor barrier the moisture is contained and can be removed by turning the vapor barrier inside out and shaking off the flakes as the moisture freezes. Used properly, a vapor barrier liner can allow you to sleep comfortably in temperatures 10 or 15 degrees lower than you could without a liner; used improperly, a vapor barrier liner leaves you sleeping covered in your own sweat.