What Do Temperature Ratings Mean?
Temperature ratings tell you the lowest temperature at which a sleeping bag is designed to keep you comfortable. However, these ratings can be confusing because different brands use different testing methods.
Important: Temperature ratings are guidelines, not guarantees. Your actual comfort depends on many factors including metabolism, sleeping pad, shelter, and clothing.
EN/ISO Testing Standards
The most reliable ratings come from standardized testing. Look for bags tested to EN 13537 (European Norm) or ISO 23537 standards.
The Three EN/ISO Temperatures
| Rating |
What It Means |
Who It's For |
| Comfort |
Temperature at which a "standard woman" can sleep comfortably in a relaxed position |
Cold sleepers, women, anyone who wants guaranteed comfort |
| Lower Limit |
Temperature at which a "standard man" can sleep for 8 hours in a curled position without waking |
Warm sleepers, men, typical advertised rating |
| Extreme |
Survival temperature - risk of hypothermia exists |
Emergency situations only - NEVER plan to use this rating |
Understanding the Ratings
When a bag is advertised as "20°F," it usually refers to the Lower Limit rating. This means:
- A warm sleeper may be comfortable at 20°F
- A cold sleeper should look at the Comfort rating (often 10-15° higher)
- The actual "comfortable" temperature varies by individual
Rule of Thumb: Buy a bag rated 10-15°F colder than the lowest temperature you expect. If you're a cold sleeper, add another 10°F.
Seasonal Categories
Sleeping bags are typically grouped into three seasonal categories:
Summer Bags (35°F and above)
- Designed for warm weather camping
- Lightweight and packable
- Often can unzip fully as a blanket
- Best for: July/August camping, desert trips, tropical climates
3-Season Bags (20-35°F)
- Most versatile category
- Works for spring, summer, and fall
- Good balance of warmth and weight
- Best for: Most campers, most trips, best first sleeping bag
Winter Bags (20°F and below)
- Maximum insulation for cold weather
- Heavier and bulkier
- Features like draft collars and hoods are essential
- Best for: Winter camping, mountaineering, cold climate travel
Factors That Affect Your Warmth
Temperature ratings assume ideal conditions. These factors significantly impact how warm you'll be:
Personal Factors
- Metabolism: Some people run hot or cold
- Gender: Women typically sleep colder than men
- Age: Older adults often need warmer bags
- Fitness: Tired bodies generate less heat
- Hydration: Dehydration reduces warmth
- Food: Eating before bed provides fuel for warmth
Equipment Factors
- Sleeping Pad: R-value matters as much as bag rating
- Tent/Shelter: Adds 5-10°F of warmth
- Bag Liner: Adds 5-15°F depending on material
- Clothing: Base layers can add significant warmth
- Bag Fit: Too loose = cold; too tight = compressed insulation
Environmental Factors
- Wind: Increases heat loss significantly
- Humidity: Damp air feels colder
- Altitude: Higher = colder, even in "summer"
- Ground: Cold ground draws heat away
Sleeping Pad R-Value
Your sleeping pad is just as important as your sleeping bag. R-value measures insulation from the cold ground:
- R 1-2: Summer use only
- R 3-4: 3-season camping
- R 5+: Winter and cold weather
Important: A bag rated to 20°F on an R-2 pad will leave you cold. Match your pad's R-value to your bag's temperature rating.
Tips for Staying Warm
Before Bed
- Eat a snack high in fat and protein
- Do light exercise to warm up (jumping jacks)
- Change out of sweaty clothes
- Use the bathroom
- Wear dry base layers and socks
During the Night
- Cinch the hood and draft collar
- Keep head and face covered
- Put a hot water bottle in the footbox
- Eat a snack if you wake up cold
Equipment Tweaks
- Add a sleeping bag liner (5-15°F boost)
- Wear an insulated jacket to bed
- Use a higher R-value sleeping pad
- Double up sleeping pads
Quick Reference Chart
| Expected Low Temp |
Warm Sleeper |
Cold Sleeper |
| 50°F+ |
50-60°F bag |
40-50°F bag |
| 40°F |
40-45°F bag |
30-35°F bag |
| 30°F |
30-35°F bag |
20-25°F bag |
| 20°F |
20-25°F bag |
10-15°F bag |
| 10°F |
10-15°F bag |
0-5°F bag |
| 0°F |
0°F bag |
-10 to -15°F bag |