Sleeping Bags and Insulation
Simply put what makes the most effective insulation is lots of small pockets of air, wrapped around us, which will trap any heat released from our body. The more pockets of air and the more ‘layers’ of those pockets, the warmer we will stay. Think fine wool fibres, big fluffy quilts, basically anything which traps lots of pockets of air which you have experienced. An ‘insulated’ jacket or sleeping bag won’t ‘get’ you warm, but it will maintain a higher level of warmth for as long as possible.
Down or Synthetic Fill
Down is lightweight and offers a greater warmth to weight ratio. However, if it gets wet or damp it becomes ineffective as the feathers can’t ‘loft’. It is possible to clean a down bag, however it is quite a long winded process to do it yourself. There are various companies offering this service thankfully for a small fee. Finally it shouldn’t be stored packed in a stuff sack. To maintain the life of the bag, it needs to be stored uncompressed.
Synthetic bags tend to have a lower warmth to weight ratio and therefore to achieve the same insulation rating as an equivalent down bag, they use more insulation ‘fill’, which means as a result they are heavier and bulkier. However on the plus side, you can treat them fairly hard, they will still maintain a certain degree of insulation when wet and of course, they are much simpler to clean yourself.
Traditionally bags are sold with a ‘season rating’.
1 Season - Summer
2 Seasons - Summer and warmer nights in late Spring and early Autumn
3 Season - Spring through to the end of Autumn, possibly into Winter use
4 Season – All the seasons
4+ Season – All of the above and then some. Mainly for high Mountain / Polar extreme use
Traditionally users have chosen a sleeping bag to suit their needs and balanced weights and bulk accordingly. However in recent years backpackers are choosing to carry a lower ‘rated’ bag (less bulk/weight) and wear insulated clothing inside to ‘top up’ the rating. The logic is sound, as you tend to put on warm insulated clothing when you get into your shelter. So why not keep warm and slide into your bag when needed, thus keeping all the residue heat around you, instead of taking clothes off and getting cold again.
Temperature ratings quoted by suppliers in the past could vary considerable between manufacturers in different countries. Increasing efforts are in place to regulate the test results of sleeping bag warmth across Europe and America. So hopefully this will make it easier for the consumer to make direct comparisons.
Currently many sleeping bags are rated with the following headings;
Comfort Limit of Comfort Extreme
This is crudely interpreted as;
Comfort = Comfort temperature is the lowest range of temperatures at which you will get a full night of good sleep.
Limit of comfort = the coldest you will have a full night of sleep without waking from the cold.
Extreme = the coldest you could use a sleeping bag without being at risk of hypothermia. This is usually defined as getting 6 hours of uncomfortable sleep but it is not recommended for use by normal consumers. It is based on fit, well, conditioned young men, soldiers, outdoor instructors and mountaineers!