Birds have broadly 3 types of feathers. Flight feathers (do what they say), contour feathers (these are the ones that are like flight feathers on the top but towards the base become more fluffy) and down feathers (these are the best to use as they are tiny, soft and grow continuously on the bird even after being harvested).

Down is an excellent thermal insulator due to its ability to trap lots of small pockets of air. It is these small pockets which insulate us so effectively. This is why it is used for sleeping bags combining insulation with minimal weight and compressible bulk. Down bags tends to be more expensive than synthetic because it is a natural product that needs to be collected using manual labour, not manufactured with a machine. As with anything, the quality of down can vary depending on several different factors.

Down is rated using the term ‘Fill Power’. The higher the Fill Power rating ie 850, the better the down and finer the feathers sourced from a quality supply. The lower the number ie 650 the lower the grade of the down and supply source, but cheaper too.

The best down comes from duck or geese who live in colder climates such as Siberia, Eastern Europe, Canada or the Pyrenees. It is sourced from older birds that have had balanced nutrition. Finally quality down has to have been prepared, transported and graded correctly. Eg the birds need to be plucked in the spring when the down is strongest, cleanest and the natural time for birds to moult.

Harvesting the down can be mechanical when the birds are dead, by hand when the birds are dead or by hand when the birds are alive. The latter is now considered unethical and generally not used by quality sleeping bag producers, who now comply to new Code of Conduct and a Traceability Standard which European Down and Feathers Association (EDFA) members are required to follow.

The more down you have in a sleeping bag the warmer it will be. However, you also need to consider the Fill Power of a bag. This refers to the quality of the down you are putting in. The higher the number the better the quality. 800FP or more is very good. So for example the Rab Neutrino 400 weighs 805g and has a fill of 400g of down which is 800FP European Goose Down.

If other feathers are added to the fill, the insulation properties drop and so does the price! The best ratio is 95/5 which means that for every 100g of material used 95 grams will be down and the other 5 will be made up of feathers. Due to the nature of ‘sorting down’ it is almost impossible to have 100% down as trying to separate all the feathers from the down is a difficult process!


Primaloft is probably the best known brand name of synthetic filler in the outdoor arena. The fibres of Primaloft are ultra-fine and make a tight network of air pockets that trap heat from the body in just the same way as down. The fibres are also water resistant, super soft and very compressible. This naturally makes them great for use in insulated outdoor clothing as well as sleeping bags.

Climashield is another synthetic insulating material used in sleeping bags and outdoor clothing. Unlike the short staple of Primaloft, Climashield has continuous strands which are interlocked. As with Primaloft it also repels water and remains warm even it wet and humid conditions.

Alongside these two well know synthetic materials are many other. Such as Rabs own Pyrotec. However, compared to down they are all much bulkier and generally heavier.

How do you choose a Sleeping Bag?

What are you using the bag for? There is a big difference between car camping and backpacking! In other words, are you going to carry the bag yourself? In which case weight and bulk are important.

When are you using the bag, what seasons are you hoping to use it for? Does it need to be versatile and used by different members of the family and for a range of activities?

How much have you got to spend? How tall/short, (you can buy shorter and extra long bags) broad/slight, warm/cold do you sleep? The latter is quite important.

Women feel the cold differently. Women specific sleeping bags generally have more insulation round the feet and hip area

Older people who are not used to outdoor life can feel the cold more than youngsters (not including children here!)

If you have poor nutrition or hydration your body will struggle more to regulate your body temperature during the night, which is why you will always sleep warmer and better after a warm meal and being well hydrated.