Sleeping bags

Year-round I prefer down-filled sleeping bags (specifically, premium 800 fill-power down) over sleeping bags with synthetic insulations. Compared to the best synthetic insulations (like Polarguard and Primaloft), high-loft down is:

• Lighter for its warmth
• More compressible
• More breathable
• Superior in its loft retention (i.e. lifespan)

The downfall of down is that it loses its ability to insulate as it gets wet, which can happen due to condensation, perspiration, and other sources of water (e.g. rain, river fords, hydration bladder explosions, etc.). Synthetic insulations will lose their ability to insulate when wet too, though not as much. Even so, because down is such a superior insulation, even a partly wet down bag will be lighter for its warmth than a synthetic bag.

You can take measures to prevent your down-filled sleeping bag from getting wet, including:

• Buying a bag with high-loft down (which will dry quicker) and with a premium shell fabric that features excellent breathability and water-resistance (thus helping to avoid the problems stemming from perspiration and shelter condensation);
• Storing it in a waterproof stow sack or using a waterproof pack liner;
• Laying it out in the mid-day sun while taking a rest break;

It's not always possible to keep your down bag dry and in consistently wet environments (think of the Olympics in March) down-insulated garments will eventually collapse. In this case a synthetic sleeping bag would be preferable.

If the constant wetness is short-lived (e.g. a week-long rainstorm) then I will still stick with down, knowing that sooner or later there will be an opportunity to dry it out. However, I will probably take more insulation than what the conditions may suggest, because I need to account for the fact that any down-filled bag or garment will not perform up-to-par towards the latter end of the wet stretch.

Sleeping bag ratings

Forget about sleeping bag ratings for a second. Instead, think about everything you carry with you that helps you to stay warm. This includes, but is not limited to: body fat, clothing (including your rain jacket, gloves, hat, extra socks, etc.), sleeping bag, sleeping pad, shelter, and (maybe) bivy sack. If you think about it this way, you notice that already you are carrying lots of "insulation" besides your sleeping bag.

So, then, it is not necessary to bring a sleeping bag with a temperature rating that perfectly matches the nighttime low you expect to encounter. Instead, the combination of all of your insulting gear needs to match that nighttime low. This is why I take just my 40-degree GoLite Feather-lite bag even when I expect temperatures to be routinely in the mid-20's -- by utilizing all of my insulation I can stay comfortable.

My clothing accounts for a large portion of my insulation, so that I can remain comfortable during the cold parts of the day (the morning and evening, and during rest stops). If instead I took a warmer sleeping bag and less clothing, I would be equally warm at night but I would be uncomfortable during those margin times. There is a trade-off of using clothing as insulation: for the amount of materials used, most garments insulate a smaller volume of your body compared to a sleeping bag -- just consider the square yardage of fabric used in the arms of your puffy jacket versus the core section.