There are three important factors you need to consider when buying and these are temperature rating, weight versus roominess and insulation type.

Search For Temperature, Weight and Insulation

Select a bag ranked best for the coldest temperature you anticipate to come across. You can tell the temperature by the name. For example, the Marmot Plasma 15 is for temperatures of up 15°F or -9.4 Celsius.

 When backpacking, you need to keep weight low without risking comfort or safety. For many, having a light sleeping bag trumps all other factors, including sturdiness, convenience, and cost.

For other people, however, weight is less important and they prefer to have a spacious sleeping bag to have good night's sleep. Most sleeping bags aim to strike a balance between the two.

When it comes to the insulation types, you have several options: down fills, synthetic fills, and water-resistant fills.

Sleeping bags with down fills like goose or duck feathers are light, durable, compressible and breathable. They cost more initially, however, they are a great long-term investment.

Sleeping bags with synthetic insulation stand out in moist, cold weather. They also have less sticker shock. They are, however, slightly heavier, and not as compressible as sleeping bags insulated with down.

Sleeping bags with water-repellent insulation are made of feathers that have been treated resist moisture.

The EN Standard For Temperature Rankings 

Sleeping bag rankings went through a revolution, in the form of the EN temperature standard within the past few years. 

In the past, bags were rating according to comfort rating, which indicated the lowest temperature that a sleeping bag would keep a sleeper warm. So, a “20-degree” sleeping bag meant it’s intended for temperature not lower than 20 degree Fahrenheit.

However, these ratings were not at all infallible given that humans have different metabolic rates. Women have been proven to sleep colder than men.

In addition, before the EN standard, manufacturers assigned ratings based on their own research, and temperature ratings were a guide at best, not a guarantee.

The EN Rating made sleeping bag ratings more reliable. Today’s sleeping bags have two temperatures assigned to them: comfort rating for the women, and lower limit rating for the men.

Comfort rating just refers to the lowest temperature that a bag can keep an average woman warm. Lower-limit rating, on the other hand, refers to the lowest temperature that a sleeping bag can keep a man warm.

If a sleeping bag carries an EN lower-limit rating of 19°F and comfort rating of 32°F, a woman would remain comfortable within the bag as temperature falls no more than 32°F.

However, a sleeping bag’s EN rating isn't the only factor that’s going to affect your overall warmth. Other factors that can affect warmth include the sleeping pad, or the cushioning between the sleeping bag and the ground. If you are sleeping on frozen ground, use two pads.

What Affects Overall Warmth? 

A tent also affects warmth as it can trap air and warm it up. Metabolism also affects your warmth. If you’re a cold sleeper, you will want thicker insulation than warm sleepers.

In order to keep yourself truly warm inside a sleeping bag, wear long thermal underwear and sock. To help you retain heat, wear a cap and neck gaiter when you sleep. If it’s a really cold night, wear pants and a fleece jacket. Drink something warm before you sleep.

What's The Best Insulation For You?

What type of insulation should you choose? As we said before, a backpacking sleeping bag could have three types of insulation: goose and duck feather, artificial insulation, and water-resistant insulation.

Feathers are an exceptional insulator. They are light, simple to compress, and they last long and are breathable. It performs exceptionally well in cold, dry conditions or whenever you need to travel light. It is, however, expensive.

Synthetic insulation usually are usually made of a certain type of polyester. They cost less than fowl feathers and dry substantially faster. They retain a lot of their warmth even if wet. They make the perfect choice in moist environments as well as for beginning, casual or budget-minded hikers.

However, sleeping bag with synthetic insulation material is that its insulation power is reduced every time it's put back in the bag.

There's a lengthy list of competing brands that use synthetic insulation, which makes shopping for a sleeping bag confusing. However, knowing the difference between brief-staple and continuous filament should make it easier to make a decision.