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Sleeping Bags - Season Ratings Explained

Sleeping Bags are typically categorised into Season Ratings, but these ratings should only be considered as a guide and not a guarantee of the bags suitability for your needs.

The following table shows what is generally meant for each season rating.

Sleeping Bags Season Table
Although sleeping bags are grouped into season ratings you should bear in mind the following:-

  • When defining the Season Ratings, assumptions have been made regarding weather and temperature conditions for each season. In reality, of course these vary greatly from year to year and area to area.
  •  That the temperature ratings of sleeping bags are somewhat arbitrary. No universal industry standardisation exists, as yet and therefore people may disagree with the season rating the manufacturer has given the sleeping bag. (The temperature rating is relevant to the season rating).
  •  That other factors - such as the additional use of a roll or sleeping mat; are you sleeping inside a tent or completely outside and of course the thermal efficiency of any night clothing you may wear - all these other factors will affect your sleeping bag requirements.

Sleeping Bags - Temperature Ratings Explained

You will typically see two temperature ratings quoted: the Comfort Temperature Rating and the Extreme Temperature Rating. What are they? What do they mean?

The Comfort Temperature Rating - is shown as a range e.g. +12°C to +25°C. The range is generally understood to refer to the ambient temperature around you. The first temperature quoted in this range is the lowest the manufacturer considers you will remain comfortable in. Naturally, the second value is the highest temperature that they consider you will remain comfortable in.

The Extreme Temperature Rating - is a single value and is generally understood to be the coldest temperature that an experienced user should use the sleeping bag in.

Although all sleeping bags have temperature ratings you should bear in mind the following:-

  • Notions of warmth and what is a comfortable sleeping temperature are subjective. Be aware of this and let your knowledge of your own personal requirements influence your decision.
  • There are no standard measurements of temperature ratings among sleeping bag manufacturers. Use the ratings as a reasonable guide only.

Important Changes in Legislation - from 2005 some new legislation, EN13537: Requirements for Sleeping Bags- came into force. A new test to calculate the warmth of a sleeping bag is used. The regulation specifies how this warmth information is displayed to the consumer (i.e. labelling).

From the beginning of 2005, sleeping bags that meet the standard should display 4 temperature ratings:

  • Upper Limit - highest temperature at which a standard MAN would have a comfortable nights sleep without sweating.
  • Comfort - lowest temperature at which a standard WOMAN would have a comfortable nights sleep, lying on her back and relaxed.
  • Lower Limit - lowest temperature at which a standard MAN in a rolled up body posture would have a comfortable nights sleep.
  • Extreme - temperature below which a standard WOMAN could expect strong sensation of cold and maybe actual physical injury from cold (e.g. frost bite or hypothermia).

Sleeping Bags - Insulation Choices Explained

Down - is warm, lightweight and packable. If well cared for, it retains its loft up to three times longer than most synthetics. However, when it is wet, the thermal properties of down are virtually eliminated. Down forms clumps if exposed to dampness or moisture and therefore it performs best in cold dry climates.

Synthetic Meterials - the majority of sleeping bags use synthetic materials for insulation (the fill). The most common synthetic threads are usually hollow, reducing their weight and enabling them to trap more air.

The positives for synthetic fill are

  • They still provide some insulation when wet and dry fairly quickly, especially when compared to down fill. This can also mean they are easier to clean ( most are machine washable )
  • Typically less expensive than down fill
  • Allergic reactions are generally not an issue

Construction Method

The method used to keep the fill in place. It is no good having an efficient insulation material if it all ends up at one end of the sleeping bag.

The Single Layer Construction:
Stiched Through or Quilted method holds the filling in channels or baffles. However, you get cold spots along the stitch lines and therefore this method is unsuitable for cold weather bags.

The Single Layer Construction

The Off-Set Double-Layer Construction:
This method uses two layers with the the stitching lines offset helping to eliminate the problem of cold spots.

Off-Set Double-Layer Construction

The Advanced Shingle Construction Method:
This method does not use stitching at all. Because of this it typically produces 30% extra loft. Special resins enable the insulating fibres to support themselves inside the bag. No stitch lines means no cold spots.

Advanced Shingle Construction Method

Sleeping Bag Features

Zips - as well as enabling easy access, zips can be used to control temperature in the sleeping bag - particularly those fitted with, '2-way' zips. On warm nights you can ventilate the bag from the bottom, this is very handy for bags with a high temperature rating. Another aspect of zips to bear in mind is the baffle. Zips create a cold spot, so the baffle insulates it thus avoiding that cold shock sensation.

Hoods - Ever found you are all snug inside your sleeping bag but the top of your head does not feel quite as confortable - a sleeping bag fitted with a hood will come to your rescue. Many can be adjusted with the use of a simple drawcord.

Neck Baffles - the purpose of the neck baffle is to prevent the air your body has already made warm escaping. If this happens cold air drafts in particularly down the back of the neck. Typically they are adjusted by the use of a drawcord.

The Sleeping Bag Shape- essentially bags can be grouped into two shapes - the mummy shaped bags or rectangular bags.

  • Mummy Shaped Sleeping Bags - because these bags stay closer to your body and therefore have less air-space between you and the bag they are more thermally efficient. Additionally they tend to be a bit lighter because there is less material.
  • Rectangular Sleeping Bags - though less thermally efficient, for those people that like more leg room they can provide greater comfort because they cater for more sleeping positions.

Stuff Sacs - these enable easy transport and most incorporate compression straps to reduce the pack size. However, many people make the mistake of storing their sleeping bag in the stuff sac. This is bad for the filling and reduces the efficiency. For long term storage, the bag should be loose, not tightly packed.

Useful Sleeping Bag Accessories

Sleeping Bag Liners

A versatile way of adding extra wamth, making it possible to use your sleeping bag in colder conditions. Most liners are easier to clean than sleeping bags and are are made using soft materials that enhance your comfort. In warm weather, a liner alone can make a comfortable alternative to a sleeping bag.

Sleeping Mats & Mattresses

When laying in your sleeping bag the bottom insulation or 'fill' is compressed making it less thermally efficient. Additionally, the ground temperature is always  colder than your body temperature. Mattresses combat these two problems adding extra insulation just where it is needed. They also help to keep the underside of the sleeping bag cleaner.