Sleeping bag temperature ratings explained

Sleeping Bag Temperature Ratings Explained

If you’ve ever shopped for a sleeping bag, you’ve likely noticed a range of temperature ratings on the labels. These numbers—often split into “comfort,” “limit,” and “extreme” ratings—are meant to guide you in choosing the right bag for the conditions you’ll be sleeping in. But what do these ratings actually mean? And how can you ensure the bag you choose will keep you warm without overheating?

In this guide, we’ll break down the different temperature ratings for sleeping bags, explain how they’re tested, and give you tips on choosing the best sleeping bag for your outdoor adventures.

Understanding Sleeping Bag Temperature Ratings: Comfort, Limit, and Extreme

Most sleeping bag manufacturers follow a standardized temperature rating system known as EN 13537 or ISO 23537. These international standards help provide consistent information, so you can compare sleeping bags across brands with confidence. Here’s what the different ratings mean:

1. Comfort Rating
   The comfort rating indicates the lowest temperature at which the average cold sleeper (usually a woman) can sleep comfortably in the bag. This is the temperature you can rely on for a good night's sleep without shivering or needing extra layers.

   Best For: General outdoor use where you want reliable warmth. If you’re a cold sleeper, the comfort rating is the best indicator for you.

2. Limit Rating
   The limit rating is the lowest temperature at which the average warm sleeper (usually a man) can sleep without feeling uncomfortably cold. While you might not feel cozy, you should be able to sleep through the night without significant discomfort.

   Best For: More experienced campers or those who tend to sleep warm. This rating is often used by hikers and backpackers looking to reduce weight by choosing a lighter bag.

3. Extreme Rating
   The extreme rating is the lowest temperature at which the bag will keep you alive—but not necessarily comfortable. This rating is typically for emergency survival situations only, where you’re unlikely to sleep well but can avoid life-threatening hypothermia.

   Best For: Understanding the bag's absolute limits in emergency situations. The extreme rating is not recommended for regular use; it’s more of a survival benchmark.

Example of Temperature Ratings on a Sleeping Bag

Let’s look at a hypothetical example of temperature ratings for a sleeping bag:

• Comfort: 0°C (32°F)
• Limit: -5°C (23°F)
• Extreme: -20°C (-4°F)

This bag would be comfortable for most people down to 0°C, acceptable for warm sleepers or experienced campers at -5°C, and capable of keeping you alive in a worst-case scenario down to -20°C. However, you’d only want to rely on the extreme rating in a true emergency.

How Are Temperature Ratings Determined?

The EN and ISO standards use a controlled environment to test sleeping bags, taking into account factors like heat retention and insulation. During testing:

• A mannequin dressed in a base layer is placed in the bag.
• Sensors measure heat loss to calculate temperature ratings.

These tests help ensure consistency across products. However, keep in mind that everyone’s tolerance to cold is different. Factors like metabolism, clothing, and sleeping pad insulation can impact how warm you actually feel in a sleeping bag.

Factors That Affect How Warm You’ll Feel

Even with temperature ratings as a guide, several other factors influence how warm you’ll actually feel when camping:

1. Gender and Body Type
   Women generally feel colder than men at night, so they may want to choose a sleeping bag with a comfort rating that matches the expected temperature. Smaller or leaner individuals may also feel colder since they retain less body heat.

2. Metabolism and Personal Preferences
   Some people naturally sleep warm, while others sleep cold. If you’re someone who often needs extra blankets, consider choosing a bag with a lower comfort rating than the expected temperature.

3. Clothing and Layering
   Wearing thermals or adding an insulated sleeping bag liner can extend the warmth of your sleeping bag. In colder conditions, adding layers can help you feel comfortable in a bag rated slightly below the temperature you’ll be camping in.

4. Sleeping Pad Insulation
   Your sleeping pad plays a major role in keeping you warm by insulating you from the cold ground. Sleeping bags lose significant warmth when there’s no barrier between you and the ground, so investing in a good sleeping pad with a high R-value can make a big difference.

5. Humidity and Wind
   Wet or windy conditions can make it feel colder than the actual temperature. A waterproof or water-resistant sleeping bag shell can help protect you from dampness, while sleeping in a sheltered area can reduce the impact of wind.

Choosing the Right Sleeping Bag Based on Temperature Ratings

Here are some general guidelines to help you pick a sleeping bag based on the conditions you’ll be facing:

• Summer Camping (15°C / 59°F and above)
  Look for a lightweight bag with a comfort rating around 10°C to 15°C (50°F to 59°F). These bags are often more compact and easy to carry, making them ideal for warm-weather backpacking.

• 3-Season Use (0°C to 10°C / 32°F to 50°F)
  For spring, summer, and fall camping, a sleeping bag with a comfort rating around 0°C (32°F) should be suitable. This type of bag offers versatility across a range of conditions without being too bulky.

• Cold Weather (Below 0°C / 32°F)
  For late fall or winter camping, look for a sleeping bag with a comfort rating below 0°C. Bags rated for -5°C to -10°C (23°F to 14°F) are popular for cold-weather campers.

• Extreme Cold (Below -10°C / 14°F)
  For high-altitude or winter expeditions, you’ll need a heavy-duty sleeping bag rated well below freezing, often with comfort ratings around -20°C (-4°F) or lower. These bags are usually bulkier and feature advanced insulation to handle extreme conditions.

Tips for Staying Warm in Your Sleeping Bag

No matter what bag you choose, here are some extra tips to stay cozy during your night outdoors:

• Warm Up Before Getting In: Do some light exercise to warm your body up before getting into your bag. Avoid getting in while already cold, as it can take longer to warm up.
• Use a Sleeping Bag Liner: A liner can add up to 10°C (18°F) of warmth, making it a useful accessory for colder conditions.
• Wear Dry, Warm Clothes: Change into dry base layers before sleeping. Wet or sweaty clothes can make you feel colder.
• Insulate Your Head and Feet: Your extremities lose heat quickly, so consider wearing a hat and warm socks if it’s especially cold.
• Close the Hood and Draft Collar: Many cold-weather sleeping bags have hoods and draft collars to trap heat. Use these features to prevent warm air from escaping.

Final Thoughts: Understanding Your Ideal Sleeping Bag 

Choosing the right sleeping bag temperature rating is all about matching the bag to your needs, environment, and personal comfort level. If you tend to sleep cold, focus on the comfort rating; if you sleep warm, the limit rating may be enough for you. And always remember, the extreme rating is a survival metric, not a measure of comfort.

If you’re gearing up for a new adventure and need help finding the right sleeping bag, keep these ratings in mind, and consider your own sleeping habits and the expected weather. A well-chosen sleeping bag can make the difference between a restful night’s sleep and an uncomfortable, chilly experience.

Happy camping, and stay warm!