What is the difference between the Altos-S and Altos Down?Updated 2 years ago

The biggest differences are their compressibility and their actual warmth factor. My notes say that the down bag is 15.5" x 9" x 9" when packed (not compressed) and the ALTOS-S is 14" x 8" x 8" when packed. Down typically compresses better than synthetic, so you may actually be able to fit the down bag into tighter spaces, even though it is technically larger when packed.

When it comes to warmth, that's the real difference. We put our LEEF and our ALTOS down bags through a third party testing process called an EN rating. This gives us the temperatures at which the average female body is comfortable (comfort), the average male body is comfortable (limit), and the temperature at which the average female body can be protected from hypothermia (extreme).

The EN ratings for the ALTOS 0 are as follows:

• Extreme: -29F/-34 C
• Limit: 7 F/ -14 C
• Comfort: 19 F/ -7 C

As with many other sleeping bag companies, we do not have all our bags EN rated. The process is quite expensive, and we try to keep our costs low to provide our adventurers great gear at more accessible prices. The temperature rating for the ALTOS-S is a factory rating. To be safe, we consider the factory rating to be an extreme rating (-18 C), though it will likely perform well in a range around the given rating with the proper pad and layering system.

Ultimately, the ALTOS down bag is likely to be warmer than the synthetic for its rating.