Sleeping bag temperature ratings: what you need to know for a comfortable night on a trip

The temperature rating of a sleeping bag is one of the things that decides how comfortable and how safe a night outdoors will be. Misreading that rating, or ignoring it, can lead to more than an unpleasant night: it can lead to serious health problems. This article looks at how to choose a sleeping bag, how to get the most warmth out of the one you have, and what else makes a night more comfortable.

What is a sleeping bag temperature rating?

The temperature rating of a sleeping bag is the range in which the bag gives you a comfortable night. Manufacturers usually quote three figures:

1. Comfort temperature – the lowest temperature at which an average person feels comfortable.
2. Limit temperature – the lower boundary at which you can still sleep in the bag without becoming chilled, though in less pleasant conditions.
3. Extreme temperature – the level at which a short sleep is possible without risk to life, but with a risk of hypothermia.

Why the warmth of the bag is not always the deciding factor

Choosing the right rating matters, but it is only one element in the system that keeps you warm. In practice the warmth of the sleeping bag comes fourth in order of importance. First comes preparing your body properly:

1. Food and water. Get into the bag fed and hydrated. That keeps your body producing heat from the inside.
2. Movement. If you feel cold before you turn in, do a few squats or some brisk movement to warm up.
3. Staying dry. Never get into a sleeping bag in wet clothing. All it does is take heat away from you.
4. The quality of the bag. Choose a bag that matches the temperatures you will meet.
5. Extra heat sources. A bottle of hot water makes a real difference to comfort.

The hot water bottle: how to use it well

A hot bottle is not just a convenient way to warm up, it is an important addition to your sleeping bag. Used properly, it can raise the comfort of your bag by 10 degrees!

How does it work?

1. Fill the bottle with boiling water. High in the mountains water boils at a lower temperature, so it is almost impossible to scald yourself.
2. Put the bottle at the foot of the sleeping bag. That warms your extremities, the most vulnerable part of the body.
3. Use a good bottle, such as a Nalgene. These bottles are made from a special plastic that holds the heat for 5-6 hours without burning you.
4. If your bottle is metal, make sure the outside is warm rather than hot.

How to improve the insulation of your sleeping bag

1. Put a blanket over the top. In the mountains and in huts there is almost always a spare blanket to be had. Ask for one if you cannot see it.
2. Keep your feet warm. Down socks or purpose-made camp booties are ideal for this.
3. Insulate from below. A good mat or inflatable mattress stops heat escaping into the ground.
4. Do not overheat. If you get too hot you start to sweat, and damp clothing or a damp bag loses its insulating power.

Advice for women

Women usually feel the cold more, so a few points are worth keeping in mind:

• bags with a narrower cut or extra insulation around the feet;
• a hot water bottle, particularly in combination with a women’s bag;
• metal flasks with a warm body, which can serve as a heat source overnight.

In conclusion

The temperature rating of a sleeping bag matters, but do not forget the other factors: being fed, moving before bed, staying dry, and having extra sources of heat. A hot water bottle is more than a practical trick — it is a way to make the night substantially more comfortable. Sensible preparation and sensible use of your kit will let you enjoy any trip, even in the hardest conditions.

May your nights be warm!