For a long time down sleeping bags has been the most common choice for people going trekking. However, as synthetic bags have improved, especially after Fjällräven launched Supreme Microloft Sleeping bags, they are now seen as a serious option. In short down sleeping bags provides outstanding insulation for very little weight, and can be compacted into very small sizes However, synthetic-fill bags cost less, and a wet synthetic bag works better than a wet down bag
Down slepping bags
Down sleeping bags are very warm, comfortable and thermostatic. This means that a down sleeping bag will keep you warm in the cold and cool in the heat. Down filled bags main advantages are that they are very light and have a higher weight to warmth ratio than the synthetically filled bags. They do compress well into small rolls and tend to have a significantly increased service life over synthetic fills.
Down sleeping bags are graded in accordance with what is called the fill power. Fill power is a measure of the loft or "fluffiness". It is measured in the number of cubic inches one ounce of down will displace. The higher the rating numbers the better the insulation value. A down sleeping bag made with higher fill power is lighter and more compressible than an equally warm one made with lower quality down. A fill power of 400–450 is considered medium quality, 500-550 is considered good, 550–750 is considered very good, and 750+ is considered excellent.
The disadvantage of a down sleeping bag versus a synthetic bag is that they lose some or most of their insulating properties when they become wet. That is why you need to keep your down sleeping bag as dry as possible. If your down sleeping bag does become wet, it will also take quite a while to dry out properly.
Another initial drawback to a down sleeping bag could be that they generally cost more than synthetic sleeping bags. However, being more expensive this is often made up by a much longer life. If you care about your equipment, a down sleeping bag will last about 10-15 years.
Synthetic - Supreme Microloft
The synthetic fibers in Supreme Micro Loft material have been developed in cooperation with Fjällräven and are one of the best synthetic fibers that exist today. It is a combination of thin and slightly thicker silicon-treated microfibers that fills the sleeping bag with air, which in turn provides insulation. The principle is the same as with down padded sleeping bags. Thanks to an ability to retain their shape even after long-term use, the synthetic fibers are an excellent alternative to down. The synthetic fibers also withstand moisture better and retain their thermal properties even after getting damp.
The shortcomings about these bags compared to our down sleeping bags are that they are bulkier and weigh a bit more.