As backpackers, hikers, and campers, we tend to be a bit obsessive over gear. We spend hours and hours researching, reading about, and debating the best gear for our respective outdoor hobbies. While there are differing opinions on what to invest your money in, every adventurer agrees that a quality sleeping bag is an absolutely essential piece of equipment for every outdoor kit.

But before you go out and spend hundreds of dollars on a quality sleeping bag, first, you need to determine what temperature bag will best suit your outdoor needs. This comprehensive guide will help you find the perfect sleeping bag and maybe even a few sleeping accessories that will keep you dry, warm, and comfortable on your next adventure.

If it's your first time buying a high-quality sleeping bag, you may find yourself getting overwhelmed by temperature ranges and terms like "ISO tested." Don't worry, though. It's not as complicated as it seems. So let's break it down from the beginning; what are temperature ratings?

Until recently, sleeping bag manufacturers conducted all of their thermal testing in-house, which caused a lot of inconsistency in relation to temperature ratings across the board. For example, In their tests, some brands factored in the use of outer-layer clothing while others did not. This meant that even though two different brands gave their bags a 32-degree temperature rating, the fill material, weight, and price could be drastically different, making it extremely difficult to compare models accurately from competing manufacturers.

So in 2005, in an effort to eliminate this confusion, the EN 13537 (European norm) standard was introduced for sleeping bags sold and manufactured in European countries. EN standard testing utilizes a thermal mannequin to determine four temperature ratings: upper limit, comfort, lower limit, and extreme. These tests assume that the sleeping "subject" is wearing nothing more than thermal underwear and is using a sleeping pad under their sleeping bag.

• Upper limit: The temperature at which an average male (age 25, height 1.73M, weight 73 kg) can sleep without experiencing excessive sweating. The temperature is calculated with the sleeping back hood and zippers open.
  
  

• Comfort: The temperature at which an average female (age 25, height 1.60M, weight 60kg) can sleep comfortably in a relaxed position.
  
  

• Lower limit: The temperature at which the average male can sleep undisturbed for eight hours in a curled position.
  
  

• Extreme: The minimum temperature at which an average female can sleep for six hours without risking death from hypothermia.

While the EN rating system still exists, the ISO 23527 (International Standards Organization) standard has become more widely implemented since it was designed for international use and is more accurate to real-world conditions. ISO testing is conducted in a temperature-controlled third-party facility with a thermal mannequin wearing a hat and socks in addition to base layer thermal underwear.

After ISO has tested a sleeping bag, they will rate it with two numbers. These are the ratings you'll see on the packaging of sleeping bags while shopping.

Comfort rating

The higher number (typically the number on the left) indicates the ISO comfort rating or the lowest temperature that your average "cold" sleeper will be comfortable in the sleeping bag. Because women generally sleep colder than men, the comfort rating is often referred to as the "women's temperature" on unisex bags.

Lower limit rating

The lower number (typically located on the right) is the lowest temperature that the average "warm" sleep will be able to sleep comfortably through the night. On unisex sleeping bags, this is sometimes labeled as "men's temperature."

Another thing you may notice while browsing the shelves of your local outfitter is gender-specific sleeping bags. Manufacturers consider temperature tolerance, size, and shape when designing men's and women's sleeping bags.

Temperature tolerance - Because of the natural temperature differences in males and females while sleeping, men's sleeping bags are generally based on the lower limit rating. In contrast, women's bags go off of the comfort rating. According to REI: "Data on physiological differences between traditional genders has always shown that the "average woman" will feel colder in the same bag than the "average man" will feel. So, the comfort rating, which is the temperature for colder sleepers, was the logical spec target for women's bags, and brands continue to use the comfort rating on women's bags today."

To put it simply, If you tend to get warm while you sleep, a men's bag is likely the choice for you, and if you get cold easily, you'll probably be better off with a women's sleeping bag. Just remember that because women's bags are based on comfort level, they tend to be a bit heavier than men's bags rated for the same temperature.

Size and shape

Men's bags tend to be longer and broader, while women's sleeping bags are typically wider at the hips and more narrow through the shoulders. Creating gender-specific bags that cater to the physiology of each respective sex Allows manufacturers to minimize unnecessary air space creating the best possible heat regulation.  

Now that you know how to read the EN and ISO temperature ratings, it's time to choose a sleeping bag. Here are three tips to keep in mind before you make your final decision.

It's always better to have too much than not enough when it comes to thermal protection. If you get too hot in your bag, you can always open it up to allow cool air in. However, it doesn't work the other way around. If you get cold, there's only so much you can do to warm up. So, keeping this in mind, a good rule of thumb is to choose a bag rated for temperatures 15 degrees lower than what you plan to experience. Then, if the air temperature changes unexpectedly, you'll still be warm and comfortable.

Air temperature is one thing, but when you throw factors such as rain or snow into the mix, your comfort and even safety may be jeopardized. So, it would be best if you opted for a bag filled with the appropriate insulation for your planned climate. Down insulation is lightweight, compresses easily, and is excellent for dry cold conditions. Synthetic fill is a heavier material. However, it dries out quickly and insulates well when wet.

It's your sleeping bag's job to capture and retain the warmth emitted from your body to keep you warm throughout the night. The shape you opt for will significantly impact the bag's ability to keep you warm. Generally, sleeping bags come in three shapes.

• Mummy - Mummy bags are slim, lightweight, and conform to the sleeper's shape. This style of sleeping bag is the most efficient at retaining warmth because there is less dead space to heat than in other styles.

• Rectangular - Rectangular sleeping bags are often the solution for sprawlers, side sleepers, and those who don't like the confined feeling of a form-fitting mummy bag. While not as efficient at heat retention, rectangular bags allow a sleeper to shift comfortably into whatever position they find most comfortable.

• Barrel - Barrel bags, also called "semi-rectangular" or "modified mummy," are a great middle-ground between mummy and rectangular shapes as they offer enough room to move freely within the bag while maintaining the heat retention properties of a slim, hooded bag.

Sometimes, the best part of an adventure is the unknown. However, when it comes to the weather, unexpected changes in temperature and conditions can spell disaster for an unprepared camper. So, before your next big trip, it's important to ensure that your sleep system is fully equipped to handle varying conditions.

Along with your bag and sleeping pad, no sleep system is truly complete without a removable sleeping bag liner. Quality liners are affordable, compact, and can add up to five degrees of extra warmth to a sleeping bag, making them a versatile addition to any adventure kit.

Climbers, backpackers, and hikers often experience sudden drops in temperatures as they ascend higher into the mountains and often struggle to sleep comfortably at higher altitudes. Fortunately, removable liners provide a solution to this problem. Having the ability to add or remove a liner adds extra flexibility to a sleeping system and allows a sleeper to adapt to changing climates.

Remember that manufacturer-provided temperature ratings, gender suggestions, and sleeping bag shapes are guidelines, not hard rules. The perfect bag is the one that fits your needs. So be careful not to limit yourself to one specific brand, gender, or style. Also, if you're struggling to wrap your mind around temperature ratings, you can always add a removable sleeping bag liner for extra warmth and versatility. Check out Cocoon's extensive line of sleeping bag liners here.