1. Weight

Weight is a top priority for ultralight backpackers. Every ounce matters when you’re carrying all your essentials on your back. Ultralight sleeping bags typically weigh between 1 to 3 pounds, but the exact weight will depend on the insulation type and size. Opt for a bag that balances weight with warmth—cutting weight at the expense of adequate insulation can lead to uncomfortable nights. Always check the packed weight listed by the manufacturer and consider if you’re willing to compromise a few extra ounces for added comfort.

2. Insulation Type

The insulation in a sleeping bag is what keeps you warm. There are two main types: down and synthetic. Down insulation, made from duck or goose plumage, is known for its superior warmth-to-weight ratio and compressibility. However, it can lose its insulating properties when wet. Synthetic insulation, often made from polyester fibers, is bulkier but performs well in damp conditions and is generally more affordable. Consider the climates you’ll be exploring and whether moisture resistance or packability is more critical to you.

3. Temperature Rating

The temperature rating indicates the lowest temperature at which the bag can keep you warm. Always choose a bag with a temperature rating suitable for the coldest conditions you expect to encounter. Most sleeping bags have a "comfort" rating (for a cozy sleep) and a "lower limit" rating (where you’ll stay alive but not necessarily comfortable). Be mindful of your own tolerance for cold; if you’re a cold sleeper, opt for a bag rated a few degrees lower than your anticipated conditions.

4. Shape and Fit

Sleeping bags come in various shapes, including mummy, rectangular, and semi-rectangular. Mummy bags are the go-to for ultralight backpackers due to their snug fit and efficiency in retaining body heat. Rectangular bags offer more space to move but can be bulkier and less efficient in colder temperatures. Semi-rectangular bags strike a balance between the two. Also, ensure the length and width fit your body size—a bag that’s too large can leave you with cold spots, while one that’s too small will feel restrictive.

5. Materials and Durability

The outer shell and lining materials affect both the bag’s weight and durability. Most ultralight sleeping bags feature ripstop nylon or polyester shells that are lightweight yet resistant to tears. Look for bags with a DWR (durable water repellent) finish for added protection against moisture. The lining should feel comfortable against your skin, so test for softness if possible. High-quality zippers and stitching are also critical for long-term durability, especially for frequent travelers.

6. Compressibility and Packed Size

If you’re traveling light, the sleeping bag’s packed size matters just as much as its weight. A bag that compresses down into a compact size saves space in your backpack for other essentials. Down-filled bags typically pack smaller than synthetic ones, but compression sacks can also help reduce bulk. Consider how the bag fits into your overall packing strategy.