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How Warm Is A Sleeping Bag?

When camping, sleeping bags are the obvious way of enjoying a warm and comfortable night's sleep. Cold spots are eliminated as the fill, natural or synthetic, wraps around trapping still warm air for insulation. Assessing warmth by the seasons is useful but Spring in Devon is likely to be far warmer than the same time of year in the north of Scotland plus, of course, some people sleep warmer or colder than others. On top of that, gender, weight and fitness are considerations and the seasons themselves vary from year to year. However, seasons are still useful before considering more detailed ratings - 1 season: Summer 1-2 seasons: late Spring - Summer; Summer - early Autumn 2-3 seasons: Spring - Autumn 3-4 seasons: Spring - Winter The EU standard (EN13537) is a testing and rating system that enables you to compare sleeping bags and will give you a fair idea of how warm a bag will be in use. As you might expect, the detail is complicated!  Using a dummy with thermal sensors, the insulation value is calculated to give four temperature values - upper limit, comfort, lower limit and extreme - based on use by average weight people (men - 80kg; women- 65kg). Results are collated for each sleeping bag, based on the air temperature outside the sleeping bag, which allows you to assess the comparative performance of sleeping bags before buying. EN 13537 guidelines: •  Upper Limit or Maximum Temperatureis the highest temperature at which a ‘standard’ adult male is able to have a comfortable night’s sleep without excess sweating. • Comfort ratingis based on a ‘standard’ woman having a comfortable night’s sleep. • Lower Limitis based on the lowest temperature at which as ‘standard’ adult male is expected to be able to have a comfortable night’s sleep. • Extremerating is a survival-only rating for a ‘standard’ adult woman. Top tips for warmth A sleeping bag is not warm - it is your body heat that warms the air in the insulating fill. The warmer you are when you get your head down, the faster your bag will warm up: Spread out your sleeping bag when the tent is pitched so it can loft fully. Holding the mouth of your bag in both hands, blow air into it by using a bellows-style action to help the fill loft and air off. Insulate yourself from the ground with a sleeping mat. A hot meal will boost your body temperature as will even a short walk. We breathe out a lot of moisture so, as all fills start to lose their performance when damp, avoid burrowing into your bag; make sure the hood is held snug around your ears. Wear fresh socks to bed; a pair used only for bedtime. Have a beanie-style hat handy if your bag does not have hood. If you are concerned that the temperature might drop sharply during the night, keep a light blanket to hand for extra insulation.
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