Miya Pearson
Sleeping bag temperature ratings are a complicated topic. The ISO 23537 standards base the Comfort rating on a standard woman who is not shivering in a relaxed posture. The lower Limit rating is based on a standard man who is curled up inside the sleeping bag and not shivering. The numbers can be presented differently by brands, and there are additional ratings that are generally unhelpful. For example, the EN rating has an 'extreme' rating, which means a woman will not die of hypothermia within 6 hours at that temperature. The bag industry has agreed to test bags the same way for all brands, with most brands sending their sleeping bags to an independent test lab that assigns bag temperature ratings. The ISO (International Standards Organization) oversees bag testing, which is almost identical to the EN (European Norm) bag test. However, real-world comfort may not match lab-tested temperature ratings due to various factors such as clothing, body type, weather conditions, and food. The Premium Warm Lightweight Envelope Sleeping Bag (200 GSM) by Active Era is an example of a sleeping bag with a temperature rating of 200, keeping users warm at temperatures down to 15°C and with an extreme limit of -3°C.
| Characteristics | Values |
|---|---|
| Temperature Rating | 20°F (-6°C) or 200 GSM |
| Usage | Three-season camping, indoor use, sleepovers, or outdoors during the summer |
| Features | Contoured hood, draft tube along the zipper, footbox design, rip-resistant, water-repellent outer shell |
| Weight | Lightweight |
| Cleaning | Machine washable |
| Shape | Envelope-shaped or mummy-shaped |
| Insulation | High-fill-power down or advanced synthetic fibers, insulated pads, closed-cell foam pads |
| Tolerance | Individual tolerance to cold varies |
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What You'll Learn
- Sleeping bag temperature ratings are a complicated subject
- The ISO 23537 standard bases the comfort rating on a standard woman
- The lower-limit rating is based on a standard man
- The bag industry has agreed to test bags the same way for all brands
- The best 20-degree sleeping bag balances warmth, weight, and comfort
Sleeping bag temperature ratings are a complicated subject
The temperature ratings on sleeping bags are typically based on two measurements: the "comfort rating" and the "lower limit" rating. The comfort rating indicates the temperature at which a cold sleeper might feel comfortable, while the lower limit rating indicates the temperature at which a warm sleeper might still be comfortable. The comfort rating is usually used for women's bags, while the lower limit rating is used for men's bags. This is because data shows that the "average woman" will feel colder in the same bag as the "average man".
The ISO 23537 standards define the comfort rating as the temperature at which a standard woman would not shiver in a relaxed posture. The lower limit rating is based on a standard man curled up inside the sleeping bag and not shivering. However, these ratings are just estimates, and real-world comfort may differ due to various factors. Additionally, the numbers on bag names may not match the exact temperature ratings, as brands tend to round up or down to the nearest 0 or 5 for simplicity.
Some companies, especially smaller cottage companies, use their own rating systems, which may be set to "comfortable at XºF". For example, a 20°F bag is designed to keep the average sleeper warm and comfortable at temperatures as low as 20°F (-6°C). This temperature rating is crucial for campers and hikers planning trips in cold but not extremely cold conditions. It is important to note that individual tolerance to cold varies, and factors like sleeping pads, clothing, and tent insulation can affect overall warmth.
When choosing a sleeping bag, it is essential to consider the type of insulation and the temperature rating. The insulation type can be down or synthetic, with down-filled bags offering superior warmth-to-weight ratios. However, synthetic insulation provides reliable warmth when damp and is more affordable. The temperature rating should be chosen based on the expected weather conditions, keeping in mind that the ratings are just estimates, and it is better to overshoot than to have a bag that is too cold.
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The ISO 23537 standard bases the comfort rating on a standard woman
The ISO 23537 standard bases its comfort rating on a "standard woman" who is not shivering and is in a relaxed posture. This is in contrast to the lower limit rating, which is based on a ""standard man" who is ""curled up inside the sleeping bag" and also not shivering. The standard defines a test procedure using a calibrated mannequin in a climate-controlled room on a well-insulated sleeping pad, for measuring a sleeping bag's maximum temperature, comfort temperature, limit temperature, and extreme or survival temperature.
The ISO 23537 standard was introduced in 2016 by the International Standards Organization to replace the European Norm (EN) 13537 standard and make it more consistent. The EN 13537 standard was the first widely used international standard for measuring sleeping bag temperature ratings. The ISO 23537 standard requires specific consumer labelling on each sleeping bag, including a graphic based on the four calculated temperatures. The standard also allows for the testing of hoodless sleeping bags and quilts.
It is important to note that the ISO 23537 test does not cover other features that can affect warmth, such as draft-prevention features like hoods, neck collars, and zipper draft tubes. In addition, the use of a motionless mannequin may not accurately test the draft-prevention features of a sleeping bag. Other design issues can also impact the warmth of a sleeping bag, including insulation movement and clumping, overstuffing, compressing insulation, and balancing between roominess and heat retention.
The ISO 23537-1:2016 standard does not apply to sleeping bags intended for specific purposes, such as military use or extreme climate zone expeditions. It also does not apply to sleeping bags for children or babies, as there is no prediction model for determining the limiting temperatures based on the thermal resistance of these bags. The standard is used in several countries, including Austria, Belgium, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, the Netherlands, New Zealand, Norway, Poland, Portugal, Romania, Slovakia, Spain, Sweden, Switzerland, the United Kingdom, and more.
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The lower-limit rating is based on a standard man
Sleeping bag temperature ratings are a complicated topic. The numbers on bag names do not correspond to exact temperature ratings. For instance, the Men's "Snugglebuggle" 15 Bag has an ISO lower-limit rating of 18 degrees Fahrenheit. Brands will round up or down to a number ending in 0 or 5 for simplicity, so it is always good to look at the actual test rating on a bag.
The ISO 23537 standards base the Comfort rating on a "standard woman" who isn't shivering "in a relaxed posture." The lower-limit rating is based on a "standard man" who is "curled up inside the sleeping bag" and not shivering. The numbers can be presented differently by brands. The EN and ISO tests use a heated mannequin fitted with 15 temperature sensors to represent a sleeping person. The mannequin is dressed in a baselayer top, tights, long socks, and a hat, and is placed inside the sleeping bag on top of a closed-cell foam sleeping mat inside a cold chamber. Measurements are recorded as the ambient temperature drops via the sensors on the mannequin.
The lower-limit rating is based on a "standard man" in a "curled-up" position inside the sleeping bag. This is different from the comfort rating, which is based on a "standard woman" in a "relaxed posture." The lower-limit rating assumes that the man is fighting against the cold but has achieved thermal equilibrium and is not shivering. This rating is designed to provide guidance on the warmth of a sleeping bag for a man who is sleeping in a curled-up position, which is typically how men sleep.
The lower-limit rating is always lower than the comfort rating and indicates the temperature at which a warm sleeper might still feel comfortable. This is the temperature rating used on men's bags. It is important to note that temperature ratings are estimates and not definitive guarantees. Lab testing simulates how a sleeping bag should be used, but it cannot account for all variables, such as differences in clothing, gear, body types, weather conditions, and individual variations. Therefore, the comfort level of a sleeping bag in the real world may differ from its tested temperature rating.
When choosing a sleeping bag, it is essential to consider the lowest expected temperature and your personal internal thermostat. If you often feel cold, use the comfort ratings as a baseline and select a bag with a lower comfort figure than the coldest expected temperature. If you tend to sleep warm, you may rely on the lower-limit ratings, but it is still recommended to allow for a buffer of a few degrees Celsius. Additionally, it is worth considering the weight of the bag, as a winter bag can weigh 2+ kg unless you invest in high-quality synthetic insulation.
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The bag industry has agreed to test bags the same way for all brands
The number 200 on a sleeping bag is a reference to its GSM (grams per square metre) rating. In this case, a 200 GSM sleeping bag will keep you warm in temperatures down to 15°C, with an extreme limit of -3°C. This is a comfortable option for indoor use, sleepovers, or outdoor use in the summer.
Industry-Wide Standards for Sleeping Bags
The bag industry has agreed to implement a standardised testing method for all brands. This means that, regardless of the manufacturer, sleeping bags will be assessed in the same way to determine their performance and suitability for different temperature conditions. This is important because it provides consumers with accurate and consistent information to make informed purchasing decisions.
The standardised testing approach ensures that ratings such as the one you mentioned (200 GSM) have a consistent meaning across different brands. This consistency is crucial, especially when considering the safety implications of using a sleeping bag that may not provide adequate warmth in colder environments.
The industry-wide agreement includes several key elements. Firstly, testing will be conducted by independent laboratories using standardised equipment and procedures. This ensures that all sleeping bags are evaluated under the same conditions, minimising variability between tests. Secondly, the testing protocol will adhere to ISO 23537 standards, which define specific criteria for assessing sleeping bag performance.
The ISO 23537 standards include two critical ratings. The first is the Comfort rating, which is based on a "standard woman" who is not shivering while in a relaxed posture. The second is the Lower Limit rating, which is based on a "standard man" curled up inside the sleeping bag and not shivering. These ratings provide a more nuanced understanding of a sleeping bag's warmth and suitability for different users.
By adopting this standardised testing approach, the bag industry has improved the accuracy and reliability of sleeping bag ratings. Consumers can now make more informed choices, ensuring they purchase a sleeping bag that meets their specific needs and provides adequate warmth for their camping, hiking, or outdoor adventures.
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The best 20-degree sleeping bag balances warmth, weight, and comfort
A 20-degree sleeping bag is a great all-around option for a range of conditions and backpacking trips. While it might be overkill in warm summer weather, it is ideal for spring and fall trips. The best 20-degree sleeping bag balances warmth, weight, and comfort.
The Feathered Friends Swallow 20 YF is a great premium option. It is very similar to the Feathered Friends Hummingbird UL 30 in warmth and packability, but not as comfortable. The Hummingbird UL 20 is another option from Feathered Friends, which is slightly more affordable and lighter, with trimmer dimensions. The Feathered Friends Tanager is another bag from the brand, but it lacks a hood and zipper, which the Sea to Summit Spark offers, along with a 45-degree bag that packs down to the size of a 1-liter Nalgene bottle.
For those on a budget, the Kelty Cosmic 20 is a great option. It is one of the cheaper down sleeping bags on the market, with an ISO Comfort rating of 31 degrees Fahrenheit, which should keep you warm in most 3-season conditions. It features a zippered internal pocket, a recycled nylon shell, a draft tube and collar to minimize heat loss, and multiple zippers for venting. The Kelty Cosmic 20 is also available in a down version, which is cheaper and has a better warmth rating.
The Trailmade 20 is another excellent synthetic value option. The North Face One Sleeping Bag is a versatile option with a multi-layer system that allows for three temperature ratings in one sleeping bag: 40-degree, 20-degree, and 5-degree configurations. While it is heavier and bulkier, it performs well in cold and warm camping situations and is competitively priced.
The Western Mountaineering MegaLite is another premium option, which provides plenty of room to roll over. The Western Mountaineering UltraLite is the brand's 20-degree offering, with 16 ounces of 850-fill down, a wraparound draft collar, and a full-length #5 YKK zipper. It is a great option for shoulder-season adventures and alpine conditions.
The Mountain Hardwear Bishop Pass 15 is another well-priced down option, filled with 21 ounces of 650-fill power duck down and weighing just over 2 pounds.
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Frequently asked questions
200 on a sleeping bag refers to its GSM (grams per square metre) rating, which measures the weight of the fabric. A 200 GSM sleeping bag is a good option for temperatures down to 15°C, with an extreme limit of -3°C.
A good temperature rating depends on the conditions you'll be camping in. A 20-degree sleeping bag is a versatile option for adventures in cooler conditions, but not extreme cold.
The comfort rating is based on a "standard woman" who is not shivering in a relaxed posture, while the lower limit rating is based on a "standard man" who is not shivering in a curled-up position.
Consider the type of insulation and the temperature rating. Individual tolerance to cold varies, so also think about factors like sleeping pads, clothing, and tent insulation, which can affect overall warmth.
Look for user-friendly features like a contoured hood, a draft tube along the zipper, and a footbox design that allows for natural foot positioning without sacrificing warmth.
