Down
Facts and Performance Sleeping Bags
DOWN CONTROL
Firstly, it is not the down that is keeping you
warm at night, it is the air trapped within its complex structure.
For maximum performance this combined structure of thousands of
feathers must remain stable and to do this you need down control.
This is done via the use of baffling throughout the bag and is also
used to control the distribution of down throughout the bag. Poor
baffling allows the down to shift and leaves gaps and cold spots,
causing the down to bunch up and lose its efficiency.
Baffles are generally made in two ways. The simplest is a stitch-through
baffle where the down is held between the inner and outer shell.
This is cheap to do and saves weight, but the stitching line is
an insulation weak point. The most common method is to join the
shells via strips of netting, thereby forming boxes into which the
down can then be stuffed. This is highly efficient and creates a
good insulation block around the sleeper devoid of cold spots. The
real test of a manufacturer is how they construct these baffles.
If baffles are too large, down can move around across a larger space.
Smaller baffles keep the down within a smaller area but add weight
and complexity. A good way to achieve down control is to fill the
baffles densely enough so that the friction within the baffle prevents
movement. Sufficient density can be seen when the shell fabric firmly
bulges between baffle seams.
Designers like Rab Carrington and Pete Hutchinson have pioneered
other forms of baffling like cross-baffling to reduce gravity shift
and trapezoid baffles that eliminate cold spots. Mountain Equipment's
excellent elasticized inner on their Extreme bags is a very effective
way of achieving effective thermal contact.
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Facts and Performance Sleeping Bags
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