Insulation “Quality”

[Stephan Guyenet]

Colin Fletcher writes in “Complete Walker IV” that in his opinion, there’s a qualitative difference between synthetic and down insulations of the same loft. I would say the difference might even be quantitative, with down being warmer than synthetic insulation per unit thickness. Some have said that the amount of loft is the only thing that determines insulating value, but is this really true?

If the insulation’s purpose is to restrict the movement of air, then it seems some types of insulation might be better than others, for the same thickness. Synthetic fibers are small and cylindrical, while down fibers line up in sheets that are more 2D. In theory, you’d think a bunch of thin cylinders would be just about the worst shape for restricting airflow, while thin sheets might be more effective.

What do you think?

[Richard Matthews]

Perhaps this should be expanded into self-inflating pads vs. closed cell pads.

Not all insulation is created equal.

Uniform and accurate sleeping bag temperature ratings are so difficult that they are not used on this site.

[john Tier]

Down is definately 3 dimensional ….

It is often sited that, ounce for ounce, it has the highest warmth to weight ratio of all insulations… seems to suggest an efficiency/effectiveness edge to me….

[James Schipper]

Loft is not the only determinate of insulating value. Different materials will have different efficiencies in blocking heat loss from conduction and radiation. For example as a SCUBA diver I can say that 7mm of neoprene will keep you warmer than a garment of much higher loft (it would just be heavy, uncomfortable and impermeable to water vapor). Fortunately, however, for people trying to cut weight air is a very good insulator. Essentially loft is the amount of trapped air you are insulating yourself with. The insulation does block some conduction and radiation (sleeping pads with insulation are warmer than ones that are just inflated with air). Back to the question, I don’t actually know how the synthetics and down stack up but by far the biggest determinant of warmth is going to be loft. I think performance in wet conditions and durability would be bigger considerations in choosing what type of insulation to wear.

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