From what I understood/stand it is soem "special" sail coth. I have heard Glenn from GG say that it is sail cloth. Now from my experiance of weathering a 12 inches of rain in two nights storm under a spinnshelter 3 years ago, with out even semm sealing the thing. And after reading your post I would have to say they are different spinniker materials. Hopfully they will get something up and running here shortly, Granite I love tarping it, but for the shoulder seasons I tend to dive into my SMD Lunar solo. Which is why I want to try out the GG one. Its all about weight for me now.