Hi All;
I've been looking into YLI silk for that past few days, it's available on ebay about $5.00 per 200 meter spool versus $3.50 per 30 meter spool of Pearsalls. The Yli spools fit a standard bobbin whereas Pearsalls smaller spools require midge bobbins.
Check out these flies tied with YLI silk:
http://fiberglassflyrodders.yuku.com/topic/8186
Looks to be very similar to Pearsalls.
Wayneb