1. Understanding the essential criteria

a. Comfort temperature

The first criterion to consider is the sleeping bag's comfort temperature, which corresponds to the minimum temperature at which a user can sleep comfortably. This temperature is generally indicated by manufacturers and is tested according to European standard EN 13537. It's crucial to choose a sleeping bag whose comfort temperature is adapted to the coldest weather conditions you're likely to encounter.

b. The filling: down or synthetic?

The choice of filling is also a determining factor. Down sleeping bags, generally duck or goose down, offer an excellent warmth-to-weight ratio and are highly compressible, making them ideal for expeditions where weight and space are limited. However, they lose their insulating effectiveness when wet. Synthetic-fiber bags, on the other hand, insulate better in wet conditions and dry faster, but are often heavier and less compressible.

c. Sleeping bag shape

The shape of the sleeping bag also influences its thermal efficiency. Models are generally classified into three categories: sarcophagus, rectangular and hybrid. Sarcophagus bags fit snugly around the body, minimizing the space they need to warm up, and are therefore the warmest, making them ideal for extremely low temperatures. Rectangular bags offer more room to move but are less effective at retaining heat. Hybrid models try to combine the advantages of both shapes.

2. Additional features to consider

a. Weight and compressibility

For multi-day hikes in the mountains, weight and compressibility are important criteria. A lightweight, compressible bag makes it easier to carry and manage space in your backpack. However, you mustn't sacrifice warmth for excessive weight savings, especially in extremely cold conditions.

b. Covering materials

The outer fabric of the sleeping bag must be tough enough to resist wear and tear, yet breathable enough to prevent condensation inside the bag. Water-repellent treatments can also be applied to repel water and protect the lining.

c. Zippers and other accessories

Zippers must be of good quality to avoid jamming or breaking. An insulating flap along the zipper can help prevent heat loss. Some sleeping bags also offer interior pockets to keep valuables warm and close at hand.

3. Choice according to specific use

a. Sleeping bag for mountaineering vs. trekking

Needs vary according to activity. For mountaineering, where every gram counts, a very light, compressible sleeping bag resistant to extreme cold is preferred. For trekking, you might prefer a bag that offers more space and better resistance to humidity.

b. Durability and maintenance

A quality sleeping bag is an investment for many years. It is therefore essential to choose a model whose materials and construction guarantee durability. Maintenance is also an important factor; some sleeping bags require more specific care, especially those made from down.

Choosing a sleeping bag for the high mountains is a decision not to be taken lightly. By taking into account the criteria of comfort temperature, type of filling, shape, as well as additional features such as weight and compressibility, you'll be better equipped to make an informed choice. Be sure to take your specific needs and climatic conditions into account when selecting the most suitable model, to ensure restful and safe nights in the mountains.