As is the case with ultralight backpacks, and ultralight tents, there are several options to consider when looking at ultralight sleeping bags.
When choosing an ultralight sleeping bag, the first decision that needs to be made is insulation type. There are two types of insulation used in sleeping bags, Down insulation and Synthetic insulation. Many lightweight high quality bags are manufactured by brands like MontBell, Western Mountaineering, Valandre, MontBell, and Mountain Equipment.
Down Sleeping Bags
Down insulation is the lightest, warmest, and most compressible insulation available. Unfortunately down looses its loft when it becomes wet. This makes down the best choice for drier climates. Many sleeping bag manufacturers try to solve the problem of down getting wet by using waterproof shells. Unfortunately this creates another problem, the bag getting wet from moisture inside.
Waterproof shells greatly reduce breath ability so moisture will build up inside, the insulation will slowly wilt from this. This is not really a problem for short duration trips, but on an expedition this could mean the difference between success and failure. A great way to combat this problem is either to use a bag with a breathable shell, or use a vapor barrier liner. Vapor barrier liners are a waterproof nylon sack that goes inside the sleeping bag. This keeps perspiration from getting the insulation wet. These liners also add 5-10 degrees of warmth to the sleep system. These products are made by brands like Integral Designs and Rab. These are usually only needed for cold weather camping for longer periods of time.
There are many different qualities of down on the market. For an ultralight bag you will need down with a 725 - 850 fill power rating. This measurement determines the volume one ounce of down will fill. The higher quality of down you buy, the less down is needed to achieve the same loft. Down that carries a fill power rating of 650 or higher is generally good quality down from Europe. Anything 600 fill power or less is usually from China.
Synthetic Sleeping Bags
Synthetic insulation is the best choice for wet conditions because if the insulation gets wet, loft is not affected much so it will still insulate. Another advantage of synthetic insulation is you can dry clothes out overnight inside the bag. Synthetic bags cost less but tend to weigh more and do not compress as well as down. Unless it is likely your bag will get wet down is the best choice. When choosing a synthetic insulation look for Primaloft, Polarguard, or Climashield. These tend to be the lightest weight synthetic insulations currently available.
When choosing a bag find something that will be appropriate for the temps you expect to encounter. Many manufacturers have different temperature ratings. As a general rule buy something rated for 10 degrees colder than you expect to encounter. Generally bags rated to 20 degrees are best for three season use. 30 degrees or higher would be appropriate for a summer bag depending on your locale. For winter 0 degrees or lower is an appropriate rating. This provides a bit of safety as peoples metabolisms are different and company's temperature ratings are usually a bit optimistic. A great technique is to sleep with most or all your clothes on at night. You carry the insulation anyway so you may as well get full time use out of it. This allows you to get away with a lighter weight bag.
Top Bags and Ultralight Quilts
Another popular type of sleeping bag is the quilt or topbag. These are based on the idea that the insulation on the bottom of the bag is unnecessary because the body's weight will crush it. A quilt usually has straps on the bottom and is very versatile. These work great for different temperatures because they can be easily adjusted to allow airflow or totally seal up. They can also be used on top of a three season bag in the winter. By owning two bags and using them together you can be comfortable in a variety of conditions. Top bags usually are a quilt with fabric on the bottom, or a pad sleeve. These tend to keep the wind out better while still offering very low weights. Good quilts and top bags are made by Big Agnes, Bozeman Mountain Works, Golite, and Rab.
Sleeping Bag Construction
There are numerous different constructions and designs for sleeping bags. Bags for colder weather normally have box wall baffles. These baffles use mesh netting inside to make a full box this construction is essential in reducing cold spots. For summer bags stitch through construction is often used. This means that areas where stitching has been done will have no insulation in these spots. This could create cold spots in cooler temperatures, but is lighter weight and fine for summer use.
Most bags use horizontal baffles which have been around the longest. These type of baffles allow you to shift insulation from the bottom of the bag to the top in cooler conditions adding versatility. Vertical baffles are often used in the torso area of sleeping bags. This means that the down can not shift to the sides so your core can stay warm. Mont Bell uses a unique box baffle construction so the down is unable to shift at all. This adds durability to the bag as an older bag will often have problems with the down shifting.
There are many different fabrics used for sleeping bag shells. Make sure that the fabric you choose is windproof and has a good DWR (Durable Water Repellent). For many cold weather bags waterproof/breathable shells are an option. These provide protection but decrease breath ability. We recommend getting a waterproof sleeping bag cover that can be used over the bags breathable shell. This does not add much weight and increases the versatility of your system. Most ultralight sleeping bag shells are microfiber fabrics. These are highly wind and water resistant, fairly durable and very lightweight. Weights for microfiber shells vary from 0.9-1.3 oz per square yard. These fabrics are also highly breathable and our favorite choice for a shell fabric and lining.
How does the bag fit?
Sleeping bags should fit fairly close to the body to minimize additional air space that needs to be heated up. Mont Bell solves this problem by putting elastic inside to reduce air space to heat up. Make sure there is not too much space at the feet, unless you plan to store clothing in this space. You should be comfortable inside the bag, do not get a model that makes you feel restricted or claustrophobic. You need to be able to sleep comfortably after a long hike. It is often times helpful to get a slightly roomy bag so it is possible to wear additional clothing inside the bag. Mont bell solves this problem by allowing the bag to stretch with your movements and can accommodate additional clothing.
Sleeping Bag Costs
Lightweight down sleeping bags can be very expensive, while synthetic bags cost much less. However synthetic bags do not last as long as a down bag. On average a synthetic bag may last up to 5-6 years. This is because synthetic insulation slowly degrades and breaks down every time it is compressed. Down bags when properly cared for can last over 20 years and still perform well. Down insulation does not break down with every compression like synthetics.
Sleeping Bag Care.
In order to get a good long life out of your sleeping bag, it should be well cared for. Make sure you never store your bag compressed in its stuff sack for long periods of time. Most bags come with a large cotton or mesh bag that is great for storage at home. Keep your bag dry, a wet down bag in a stuff sack is bad news. If your bag gets wet dry it as soon as possible, with a down bag try to break up the clumps of wet down.
Keep your bag clean. Many solutions are available on the market today for cleaning sleeping bags. For a synthetic bag we recommend Revivex synthetic fabric cleaner. Synthetic bags are very easy to clean. Down bags are a little bit tougher to clean. We recommend Revivex Down cleaner. Always use large front loading washers to clean sleeping bags, your home top loader will destroy the baffles. Hang dry synthetic bags. Drying a down bag is a more difficult process. Use a front loading dryer on low to medium heat, any hotter can melt the shell. Throw in a three pack of tennis balls in the dryer as well to help break up wet down clumps. Periodically pull out the bag to break up down clumps with your hands and check dryness. Do not leave the bag in the dryer longer than needed. With proper care you should get many years of service from your sleeping bag.