Whether down or synthetic, all sleeping bags rely on the filling's loft (how it recovers depth after compression) for insulation by retaining heat.

Down is the layer of fine feathers found underneath the outer feathers of adult ducks, geese, and other water birds and is an excellent insulator; it's also light, compresses very well and regains loft quickly. As a sleeping bag fill, down is popular with lightweight campers. It's also more expensive than synthetic fillings and can lose its insulation value when wet. That said, it's durable, retains its loft over time and will be worth the initial expense as it is likely it will outlive a synthetic bags lifetime. There is however a range of synthetic fills available; many of these are quite sophisticated and rival down in terms of overall performance.

Synthetic fills are made up from layers of fibres sewn to inner and shell fabric to keep them in place. Some of these fibres are hollow, mimicking animal fur in trapping warm air. As weight and bulk aren't a worry when camping with a car, shaving grams and reducing packed size aren't so important. A simple synthetic fill will be easy to care for, survive more wear and tear than a down-fill bag, and won't break the bank when kitting out the whole family.

Down fill

Positives
•  Gram for gram, down is far warmer than synthetic fills with much better warmth-to-weight ratios.
•  Although initially more expensive than synthetics, down-filled sleeping bags can last for decades. The balance between performance, weight, packed size, use and budget is up to you.
•  Keeping your sleeping bag clean by using a liner and washing your bag as needed stops the fill getting dirty and 'matting' together reducing its ability to loft fully.

•  Down is pretty good at allowing body moisture to pass through. By wicking away this moisture, down helps you stay more comfortable and cool.
•  Down compresses superbly, regains loft quickly and offers excellent warmth with little weight penalty making it ideal for lightweight camping.

Things to consider...
•  Down loses all its insulation value when wet and takes ages to dry. Bear in mind though, that the use of waterproof stuff sacks means that the old anxieties about bags getting wet are hardly relevant to most of us.
•  As down clusters will mat together when dirty and lose loft, bags may need to be washed occasionally and more care needs to be taken than with synthetics. * Please check and follow the care label carefully.

•  Down may also cause problems for some people with allergies.
•  Down is more expensive than synthetics.

Synthetic fill

Positives
•  Man-made fills are water resistant and so keep some insulation value when wet; some even actively shed water.
•  Synthetic bags dry off quickly as moisture is held between the fibres rather than being absorbed.
•  Synthetic bags cost less than down sleeping bags.
•  They are much easier to look after, being much more tolerant of errors in washing and drying than down.
•  Synthetic fills are hypoallergenic so do not affect allergy suffers.
•  The variety of synthetic fills means there is a wide range offering options in durability, packed size, weight and cost.
•  Synthetic bags are durable and more tolerant of damage; ripping the outer doesn't mean that the fill will spill.

Things to consider...
•  To achieve similar performance, synthetic bags are generally heavier and bulkier than down bags so not ideal for lightweight campers or backpackers.
•  Over time, even if you take great care, fibres will break down affecting loft and insulation; that needs to be offset by the lower initial cost.

» Back to Sleeping Bags