In article ,
Michael Bell wrote:
In message

It's interesting that both string vests and nylon tights are so
warm-keeping, when neither of them seal the skin from the air. There
must be some deep principle of aerodynamics here!

Aerostatics, actually :-(

Air is a vastly poorer conductor than almost any solid substance,
so the insulating properties of a material are primarily the
thickness of the air gap. To avoid losses by convection, the
air needs to be trapped in very small cells - hence the immense
factors for wool or down with a windproof outer.

Neither string vests nor nylon tights are particularly warm,
incidentally, but most UK conditions don't need Arctic survival
kit. Icebreaker tights are intermediate between the two.


Regards,
Nick Maclaren.