Rookie,

In the US, there are two types of Pearsalls that are currently available and there are other types that are no longer marketed that you might find on e-bay or at an antique shop or flea market. Pearsalls Gossamer is is a thread, it is made of twisted filaments of silk that are twisted together into a tiny rope. Gossamer has been around for a long time but it is a relatively thick thread by modern tying standards. It is quite beautiful and strong and easily ties flies down to about size 18 but you have to take care not to build up too many wraps. I don't think it is possible to entirely untwist Gossamer so it will lie perfectly flat but I haven't tried very hard to untwist it. It is available in a dozen colors or so. Golden Witch has the best selection of colors I have seen in the US. It is popular for wrapping cane rods. Pearsalls Marabou is a floss that is a greater diameter than the thread and is made up of several strands (two I think) of parallel silk fibers loosely twisted together. It is possible to separate the strands of floss and use them to wrap a finer diameter body on a fly or you can just use it as is and wrap all the strands together as it comes off the spool. I wouldn't want to use Pearsalls Marabou as tying thread and it would probably be tough to tie a perfectly smooth and flat body with it. I have also heard of Pearsalls stout floss (don't think you can buy it in the US) and Pearsalls Naples which is an obselete thread that I believe is thicker than the Gossamer. The Alec Jacksons floss is a pure filament floss made of paralell strands of silk which are lightly twisted together. It is possible to untwist any twist it might have and (if you are good) tie a perfectly flat, lump free body with it. It is a thicker floss than marabou and is generally used to tie larger streamer, spey and particularly salmon flies. It is possible to seperate out exactly the number of filaments you wish to use and tie a body of any thickness you want but I think most folks use it as it comes off the spool. I believe that the Alec Jacksons comes in hundreds of colors. There is a similar product available in the US called JEC floss. You can get these products from places that cater to salmon fly tyers.