Sleeping Bag Fillings

Basically, a sleeping bag comprises of a lining and an outer shell. Sandwiched between the two is the filling which can be either down or synthetic and provides the bag's insulating properties.You have probably never given it much thought but how all that is held and stitched together can make an enormous difference to a sleeping bag's ability to keep you warm.There are various different techniques for keeping the filling in place in a sleeping bag and these differ depending on whether the bag is down-filled or synthetic filled.

Synthetic Sleeping Bags

Typically, synthetic bags are constructed using either quilted layers or with shingles. The simplest technique is known as 'quilted through layers' and simply stitches through the outer shell and lining to hold one sheet of synthetic insulation in place. This simple method does nothing to eliminate cold spots and provides minimum insulation so is used for summer/warm weather use only sleeping bags. This method is sometimes referred to as 'stitch through' too.

'Offset quilted layers' is a step up from the basic and involves using two quilted layers as described above which are offset, before the whole is stitched together. This helps to eliminate gaps and cold spots resulting in a warmer sleeping bag.

'Shingles' uses smaller sized pieces of insulation which are then overlapped before being stitched in place, much like roof tiles (hence the term 'shingle'). A variation on the shingles construction is the 'wave' which creates extra insulation by using the same amount of material within the same space so that the insulating piece becomes slightly bunched or wavy.

Down-filled Sleeping Bags

Down-filled sleeping bags will typically be constructed using what are known as 'baffles'. Various different types of stitching creates sealed off pockets or chambers which each have their own portion of down contained within them. Although strictly speaking the baffle is the wall between these chambers, most people will refer to the chambers themselves as the baffles.

The idea is that the insulating down is kept where it is most needed – the baffles regulating its placement and preventing too much shifting around which might create cold spots.

'Sew through/stitch through' is the simplest construction method and the equivalent of the synthetic fill quilted through layer. Shell, liner and filling are all put in place and then stitched together. Typically this method is used for lightweight, 1-season/warm weather sleeping bags as the seams themselves lack any insulation at all while the down is free to shift around leaving possible cold spots.

Sleeping bags intended for colder weather use are usually constructed using 'box baffles'. These can be a simple box shape, slanted or trapezoid but all create a four walled chamber, usually contained within a mesh material. To add even greater insulating properties to a sleeping bag, the box baffles can be double layered and then offset.

'V baffle' construction creates triangular chambers thus allowing a greater number of baffles and an even greater control on where the down is distributed making for  a super snug bag.

And there is yet more to the whole baffle topic.

'Stretch baffles' – this describes a type of baffle, usually of the box design, which are made to flex according to the user's shape and movements in the night and give extra comfort through less restriction.

'Vertical baffles' – this describes where the stitching creates chambers which run from top to bottom of the sleeping bag as opposed to across the sleeping bag's width. It ensures there is no migration of down from top to bottom of the sleeping bag or vice versa.

'Side block baffles' – this is an inner barrier, usually placed on the side of the sleeping bag opposite the zip side, to prevent down from the top of the bag moving underneath the sleeper where it becomes compressed and loses insulating properties.

'Continuous baffles' – describes a sleeping bag construction without side baffles. Some people prefer this type of sleeping bag as it allows them to use one bag in a variety of temperature ranges. When the weather is warmer the down fill can be thinned above the sleeper and when the weather is cooler it can be shifted back again.

'Welded baffles' – some sleeping bag manufacturers, in an effort to increase warmth efficiency, water proof resistance and strength, have done away with traditional stitching altogether. Instead their bags are welded which does away with the puncture holes inevitable in stitched bags of any construction.

Differential Cut and Differential Fill

Differential cut refers to sleeping bags, almost always mummy style bags, where the inner lining is made from less material than the outer shell with the aim of reducing cold spots by promoting efficient lofting of the fill.  Differential fill refers to sleeping bags where the distribution of the entire fill is purposely irregular – usually less insulation at the bottom of the bag, greater insulation at the top