Sleeping bags · Practical choice
If a label shows several temperatures, do not shop by the lowest one. With standardized ISO/EN testing, Comfort and Limit are useful comparison points between models; Extreme is not a normal target for comfortable sleep.
The short answerRatingHow to use itComfortThe more conservative reference point; sensible if you tend to sleep cold.LimitA lower reference for a warmer sleeper; useful for comparison but with less comfort margin.ExtremeDo not use it as a target temperature for normal sleep or as the headline buying number.
Why an ISO/EN rating is more useful than one marketing numberISO 23537-1 specifies requirements and a test method for assessing thermal performance of adult sleeping bags used for sports and leisure. Standardized testing makes ratings more comparable across brands, but it still does not turn the result into a personal guarantee of warmth.REI summarizes the practical distinction this way: Comfort is the reference for an average colder sleeper, while Limit is the lower reference for an average warmer sleeper. Your real experience also depends on metabolism, fatigue, moisture, wind, food, clothing, shelter and the sleeping pad.Important: if a manufacturer shows only one temperature with no clear ISO/EN Comfort or Limit label, check how that number was derived. Do not assume it is directly comparable with a standardized rating from another bag.
The bag does not work alone: the sleeping pad is part of the systemInsulation under your body matters because the bag's fill is compressed by your weight. REI's current sleeping-pad guidance explicitly links bag temperature ratings with pad R-value: colder conditions call for better insulation underneath you.That means a bag described around 0°C can feel much colder than expected on a weakly insulated pad. Shop and plan for the whole sleep system, not just the bag fill.
A practical way to chooseEstimate a realistic overnight low for the place and season, not the daytime forecast.If you sleep cold, compare bags by Comfort.If you know you sleep warm, Limit may be useful, but keep margin for moisture and unexpected cooling.Do not plan around Extreme. It is not a target for normal restorative sleep.Match the pad to the expected cold and check its R-value.Example: you expect roughly +2°C overnightA more conservative choice is a bag whose Comfort rating is around or below that temperature, rather than one that advertises a Limit or Extreme figure around +2°C. If you are a proven warm sleeper with a well-insulated pad, you may knowingly work closer to Limit—but that is a personal margin decision, not a universal rule.Bottom line: start with Comfort/Limit, then evaluate the pad and conditions. The lowest number on the label is not the most useful number.
SourcesChecked September 10, 2026.ISO 23537-1:2016 — Requirements for sleeping bagsREI Expert Advice — How to Choose a Backpacking Sleeping BagREI Expert Advice — Sleeping Pad Buying Guide
