That is a difficult question, because the sock is made of a stiff cloth just like the guck system and what is used for your mainsail (but thinner). It is shaped in such a way that it keeps a very flat ellipical shape. However it is very flexible and when the spi goes the side can be pushed out when necessary. It never flaps in anywind and has a nice smooth and realively flat elliptical profile upwind.

I would give the sock a rough 300 mm by 150 mm rectangle or ellips as crosssection. Is about 1 foot by 1/2 foot. I snuff a 17.5 sq. mtr spi with a 8 mtr luff. However the same setup is used on the Capricorn F18 with its 21 sq. mtr. shute as well. With my spi I have no problems and I think it is better than any other I've tried except for the snuffer system used on the RS800 skiff but that was special.

Wouter