Short fibres that stick together
Hard to describe, but I mean the fabric is made of short fibres that grip each other, but with the wind flapping the duvet around the line can push fibres apart to get through the fabric, then the fibres stick back to each other. So different from something like a cotton sheet where each piece of cotton is as long as the sheet is long or wide. Back in the day there were hundreds of weaving experts on B3ta who could explain better than I can, but then the industrial revolution came and the spinner jennies took their jobs, or something.
(ersiffly, Mon 19 Sep 2016, 23:00, 1 reply)

See what you mean but still...
It's the best explanation so far but I fibres cannot be too short because they were in a criss-cross pattern as I recall which means that they had to be longer than at least one or two criss-cross sections - will investigate. Damn those spinning jennies. Up with the Luddites!
(Gusofnavarone always makes a map of france from sarnies, Tue 20 Sep 2016, 8:27, closed)