The North Face Mummy Sleeping Bags

Liner uses

• Backpacking: A mummy-shaped liner can add 5° to 15°F of warmth to your bag. It also helps your bag last longer by protecting it from dirt and body oils.

• Traveling: A rectangular liner separates you from unclean bedding. 

Liner materials

• Silk: Very light, compact and insulates in cold weather. Absorbent and breathable in warm weather. Price: moderate to expensive. 
• Cotton: Strong, durable, absorbent. Not the lightest or most compact. Price: economical. 
• Fleece and microfleece: Warmer, heavier, soft, moisture-wicking, quick-drying. Mid- and heavyweight varieties are bulky. Price: moderate. 
• Synthetics: Moisture-wicking, breathable, stretchy. Price: moderate. 
• Insulated: Adds enough warmth to greatly extend the temp range of a lightweight bag. Price: moderate to expensive. 

Understand temperature ratings
Opt for a sleeping bag with a temperature rating below the lowest nighttime temperature you expect when camping.

Choose a sleeping bag shape
There are four main shapes: rectangular, semirectangular, mummy and double. For camping, you want one that gives you room to stretch.

Decide between synthetic or down insulation

• Synthetic is more affordable, dries faster and provides warmth when damp.
• Down is lightweight, durable and compresses small.

Other features to consider
A waterproof shell, snug-fitting hood, extra zippers and even a stash pocket can add durability, warmth and function.