Selection, warmth & temperature ratings

How to choose a One Planet sleeping bag

Warmth, weight, size and price: these are the things that really count. So we’ve simplified your choices so you can now pick your bag according to temperature rating. While we’re at it, we’ve increased your choices, your input and your comfort – it’s nothing short of a revolution.

It’s simple: once you’ve decided on a sleeping bag model and temperature rating, it’s time to weigh up (or down…) your options. Most One Planet bags now come with the choice of two fills: 700-750 loft or 800-850 loft Hydrophobic Down. Both grades of duck down have been selected to meet our rigorous standards, with a durable water-repellent (DWR) treatment applied after the cleaning and sorting process. The 700-750 loft fill will produce an excellent, well-priced bag, while the 800-850 loft down will reduce its weight and packed size.

The Camp Lite and Robin Hoodless bags are filled with our 700-750 loft Hydrophobic Down. This is our best value down, perfect for applications where minimum weight and packed size are not critical.

How warm will I be?

Three things affect how warm you will be in a particular sleeping bag.

  • First is the environment: is it cold outside; what are you using for shelter; is there a breeze; what are you sleeping on?
  • Second is you: are you a hot or cold sleeper; is your metabolism fast or slow; do you sleep in the buff, rugged up or somewhere in-between; when did you last eat and drink? (And if you’re a woman, you will feel the cold more than a man: it’s not just a gender stereotype, it’s a fact.)
  • Both you and your environment make a huge difference to how warm you will be, and we can’t control either of these things. The third factor is your sleeping bag.

Comparing sleeping bags

Choosing a sleeping bag can be complicated as there isn’t a consistent, universally adopted method of rating the warmth of the bags. Many brands (including One Planet) have adopted ISO 23537-1, the international standard for sleeping bag performance, as it is a reliable, scientific rating method. However, not all manufacturers have their bags tested to this standard, so care should be taken when comparing warmth claims across brands. Bags are also tested when new and clean, with bags needing regular cleaning to maintain performance.

Temperature ratings explained

All One Planet sleeping bags are temperature rated in accordance with ISO 23537-1, the international standard for sleeping bag performance.

What is ISO 23537-1?

ISO 23537-1 is the international standard for sleeping bag performance. (It is the updated version of EN 13537, the official European standard for the labelling of sleeping bags.)

  • ‘Comfort’ rating is based on a ‘standard’ woman having a comfortable night’s sleep.
  • ‘Limit of comfort’ is based on the lowest temperature at which a ‘standard’ man is deemed to be able to have a comfortable night’s sleep. This is the figure we use in our product descriptions.
  • ‘Extreme’ rating is a survival rating for a ‘standard’ woman. According to ISO 23537-1, ‘a strong sensation of cold has to be expected and there is a risk of health damage due to hypothermia’. This is a survival rating only, and consumers should not rely on this rating for general use. The best guidelines are the comfort and limit of comfort ratings.

Testing to ISO 23537-1

Our sleeping bag range contains more than 50 models. It is impractical to test every model and size so, in accordance with the standard, we choose a cross-section of our range for testing, the results of which allow us to draw logical parallels to establish the performance of the rest of our sleeping bags. We continue to test new bags to increase our knowledge bank.

One Planet bags are temperature rated in accordance with ISO 23537-1, the international standard for sleeping bag performance. Although the testing is expensive, it removes a lot of the guess work so common with claims relating to sleeping bag warmth. The results are scientific, standardised and reliable, and the warmth of bags tested in this method can be directly and accurately compared.

The testing involves placing a heated, lifelike mannequin inside a sleeping bag in a climate-controlled room and monitoring the results to determine the bag’s comfort, limit of comfort and extreme temperature ratings. We use Kansas State University and their mannequin Simon for our testing.

(It should be noted that testing is performed on new bags containing clean down, and the performance of the bag may decrease over time. Please refer to care and use instructions for information on how to best maintain your bag.)


Many sleeping bag manufacturers make women-specific bags. We don’t. We believe the simplest, most effective way of making sleeping bags work better for women is by ensuring women have the correct sized bag, with an appropriate temperature rating. (Let’s be honest: different colours on the outside don’t change your sleep.) We now make a selection of Small bags (the Cocoon, Nitrous and Bungle) that will suit the majority of women, as well as other shorter folk.

Something else to keep in mind: women generally feel the cold more than men – it’s not just a stereotype, it’s a fact. Temperature testing is done using a ‘standard’ male as the benchmark. When reading temperature rating information based on ISO 23537-1 (such as ours), the comfort rating is the figure to look at. It’s the lowest temperature at which a ‘standard’ women will be in thermal equilibrium (i.e. having a comfortable night’s sleep).