I recently bought some of the silkspan from Easy Built Models.  I have not used it yet but it appears to be what the reviewer on the Easy Built site said:  very similar, if not exactly the same, as the medium weight silkspan we were able to get years ago from Sig or other sources.

My main use for silkspan is to cover bare wood so I never use it anymore over open bays.  That is, silkspan is not my primary material over open bays.  I use it to cover polyspan.  I use polyspan over open bays and then the silkspan over the polyspan.  Although a bit more work I like the finish I get with silkspan.  Maybe this technique requires less dope to fill the covering, maybe not.  But, no fuzzies with the polyspan and there is also a bit more protection from sanding entirely thru the covering over cap trips and other edges.

Thanks.  I ordered five sheets and some other things from them.

Five sheets?  When I bought it, it came on a roll--10' long and about 18" wide.