Is Your Sleeping Bag Lying To You? Yes and No.

Have you ever woken up in the middle of the night camping or backpacking, a little cold, and wondering why you aren’t warm in your cozy sleeping bag that should definitely be warm enough for the temperatures outside?

The answer is probably yes, and most of us have all been there.

While the world of sleeping bags is much more regulated now than, say, 40 years ago, it is far less precise than we expect or think.

But that’s not a nefarious ploy. It’s just how life is with 8 billion different people on planet Earth, all regulating their own temperature slightly differently.

What Does Your Sleeping Bag Temperature Rating Mean?

When you look at a sleeping bag’s temperature rating, you might be confused by all the numbers. I have been, too. My The North Face sleeping bag has three examples of levels. It all depends on how warm or cold you are as a sleeper.

Comfort Rating Vs. Lower Limit Rating

If you look closely at a sleeping bag’s temperature rating, you’ll see the comfort and lower limits. These are kind of what they sound like. REI writes:

Comfort rating indicates the temperature at which a cold sleeper might feel comfortable. This is the temperature rating brands use on women’s bags.

Lower limit rating (which is always lower than the comfort rating) indicates the temperature at which a warm sleeper might still feel comfortable. This is the temperature rating brands use on men’s bags.

Why they use “comfort” for women

Research has consistently demonstrated physiological differences between genders, revealing that the “average woman” tends to feel colder in the same conditions as the “average man.”

Therefore, the comfort rating, which indicates the suitable temperature for colder sleepers, was established as the appropriate specification for women’s sleeping bags. This standard remains in use for women’s bags in the industry today.

Can you Trust These Ratings?

In 2024, sleeping bags are (mostly) tested in independent labs versus the individual company literally testing them out in the wild to see how they work. In the past, you didn’t exactly know if one 20F bag from company X was the same for company Y and so forth.

The past standard was the European Norm, which has now transformed into the ISO (International Standards Organization). So, if you see EN and ISO, these are basically the same testing standards, so you can compare them equally.

There is a caveat to this. Sleeping bags designed for frigid colds or kids’ bags may not have these independently tested ratings.

a look inside the big agnes copper spur UL3 — Photo Credit: Alec Sills-Trausch/ @Alecoutside

Rounding Up or Down

Just because a number is on the sleeping bag name doesn’t automatically indicate the temperature rating for that sleeping bag. Many companies will round up or down (to a 0 or 5) for simplicity when coining their bag name. This means that a 13F bag would be marketed as a 15F.

The same goes for a 32F bag might be a 30F.

While two degrees shouldn’t make or break your decision, it is something to keep an eye on.

How to choose a sleeping bag

Where You Are Going

This is the most important aspect of choosing a sleeping bag. If you’re doing casual car camping during the summer months, you probably only need a 35-40-degree bag, and then you should have blankets on hand in case it gets chillier.

But if you plan to go backpacking at higher altitudes, I recommend a 15-degree bag, which should cover you in almost all scenarios outside of high mountain expeditions or single-digit winter temperatures.

Do You Run Warm or Cold

The next area to consider is how you sleep. At home, do you have multiple blankets, or do you only use a sheet? This can help determine if you are a warm or cold sleeper. If you do run cold, you’ll likely want a warmer sleeping bag for your adventures.

3 Tips to Stay Warm At Night

Heat a water bottle with boiling water and throw it into your sleeping bag before bed. This will warm up your bag, so you’re nice and toasty when you get in.
Spend two minutes doing jumping jacks and squats before hopping into your sleeping bag. Boosting your body temperature before bed will help warm up your bag.
Bring a light blanket, use extra clothes, or unfold a foil emergency blanket and put it under your sleeping pad. This will add another level of defense from cold air coming up from the ground and keep you warm.

Top Backpacking Bags on the Market

I personally have a 15F Ultralight bag from Big Anges, which I think makes great bags. But there are plenty of other brands that make top-tier products, too.

I’ve filtered for temperature rating and down quality.
These are the ones I’d browse.

So, Is Your Sleeping Bag Lying to You

In the end, your sleeping bag is not lying to you. It’s just almost impossible to create sleeping bags that warm every human on Earth the exact same way. There will always be variability when it comes to people sleeping, and the climate outside also affects how you feel.

So, if you’re worried about being cold, drop down five degrees, which might make the difference between shivering and feeling comfortable at night.

Until next time, adventurers, take care and be safe.

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