Nemo Equipment Thermo Gills raise the bar on bag design!! As big a deal as adding pitzips to a Gore-Tex jacket, Thermo Gills allows a single bag to have an unheard of variable comfort range. Adjust the Thermal Gills as you gain elevation, or as the weather system changes - but with the confidence you'll have the heat you need for your worst-case. Sonic™ Sleeping Bag Awarded Editors’ Choice, Backpacker, 2015 Gear GuideThere is nothing more satisfying than a good night sleep. Whether out on a quick overnighter, five days into a long backpacking trip, or bunking into a hostel or alpine hut, sleep will play a huge role in how enjoyable the rest of your trip is. There are many factors at play, including sleeping bag, mat, food, hydration and clothing. The sleeping bag is what we will focus on in this post. Sleeping bags come in all shapes, sizes, fill types, and prices. They are also labeled with these ambiguous and sometimes confusing ratings.. How do we choose the perfect bag? Like most gear, it comes down to your own personal needs for the unique trips you plan to do.
"Hoods, snorkels, zipper baffles, chest baffles, security pockets, stretch draw cords, reversible zippers, stretch baffles, channel blocks,uber light high-tenacity textiles and so on... Do any make it onto your list?"
Ratings
For a long time, sleeping bag ratings were decided by the manufacturer, with no method of standardized, third party testing to verify these claims. This led to “warm -7” bags and “cold -7 bags”, and a lot of skepticism and ambiguity. In recent years, the industry has moved to EN rating. Essentially this is a European testing standard that brings the industry a standardized method (involving a high tech mannequin equipped with temperature sensors in a lab) for testing bags. This is a little more complex than the old, single number system, but makes a lot of sense when you wrap your head around it. EN standards give the user three numbers: the first is the comfort limit for the average woman, the second for the average man, and the third number is the bottom limit of survivability for the average male. What I like about the EN standard is the fact that the bags are tested by a third party, give precise information, and hold manufacturers accountable. Rating is not everything however- keep in mind these are based on a human wearing one layer of long underwear as well as a hat. What you wear to bed goes a long way to determining your warmth and comfort.
Insulation
Sleeping bags are made with either down or synthetic insulation- both options present their own unique pros and cons with the better choice being dependent on the journey for which it is required. I am of the opinion that absolutely nothing beats the buttery soft comfort level of down. It is amazing that we can put humans on the moon but we have yet to invent an insulation fiber that can match the durability, loftiness, and warmth-to-weight ratio of down. 
Down: Generally, down bags will always be lighter and more compressible than its synthetically insulated equal. So given all this, why would someone choose synthetics? It all comes down to moisture. The one major “downer of down” is what happens when it gets wet. Damp down loses its loftiness, and with that the ability to insulate; if you get a down bag wet, you are going to have a cold night sleep. In recent years we have seen the appearance of treated down in the sleeping bag world. In treated bags, durable water repellency is added to the down filaments, with the goal of mitigating the moisture concerns of down bags. This has been met with great success, and most down manufacturers are using this technique, but it doesn’t replace the need to avoid moisture when using a down bag. A note on sourcing down: As we discussed in our previous blog post about layering, birds are never killed specifically for their down and none of the suppliers we work with use live-plucked down or force feeding. Down is a by-product of the food industry - generally the down is plucked from birds farmed for their meat. Many of our suppliers offer supply chain transparency- birds are farmed humanely, free from animal cruelty. Synthetic: Synthetic insulation- bulkier and heavier than down, is a fantastic choice for wet, humid climates. I've been in stormy conditions where even the best prepared and careful camper risks getting their down bag wet, these are situations where synthetics offer peace of mind despite their modest weight and space penalty. Mountain Hardwear uses a minimalist bag design with a unique zipper, along with their compact Thermal-Q insulation, to make a synthetic bag that packs nearly as small as down for the same weight.
Features
Hoods, snorkels, zipper baffles, chest baffles, security pockets, stretch draw cords, reversible zippers that can open from both ends or zip to another, stretch baffles, channel blocks, overstuffed foot boxes, waterproof shells, hydrophobic liners, hourglass versus mummy shapes, zipper opening gills for wide, versatile temperature ratings, uber light high-tenacity textiles that still remain down-proof and durable, warm or comfortable colours for extended stays in a tent, compression stuff bags that reduce size to a small loaf of bread – these are the tools in the quiver of an accomplished sleeping bag designer. Do any make it onto your list?
Bag shape
Most bags found on the market today are what have come to be known as mummy bags. These bags are tapered to be narrower at the feet, thus reducing the amount of dead space within the bag, resulting in a lighter and more thermally efficient piece of gear. Rectangular bags are making a comeback though, especially for hut, cabin, hostel and car camping. They are roomier, zip together, open to act as a quilt or blanket, and still weigh in pretty lightly... What’s not to like! Nemo Equipment for example has a good line of rectangular bags. 
Ultimately choosing the right bag will come down to using the right tool for the job. Think about what conditions you will encounter: what month, what season, how high, how wet, how long? Nothing is more critical to the enjoyment of your trip than getting a restful night of sleep. Reminder: hydration and being well fed have a large role in regulating body temperatures. So make sure to match that sleeping bag up to a hearty meal plan and lots of water and ensure you include an appropriate sleeping mat! Spending a lot of time in the snow and cold temps and need a warm lightweight bag - a down bag with a waterproof shell is the best choice. Hiking the West Coast Trail , or paddling maybe in the rain? It is safest to go with a synthetically insulated choice. Sleeping in hostels in SE Asia or Southern Europe? Go for comfort and ease of use, with a washable liner. The big takeaway here: the perfect bag is different for every user and every trip. A sleeping bag is a personal decision, and one person’s favorite may not be the best for everyone else. But one thing that remains constant is that absolutely nothing beats a good night sleep!