Power Pro is a gel spun polyethelene line.

It has a bit larger diameter than some others. They've added something to it or braided it in such a way to keep it more round in crossection. This is 'supposed' to help prevent dig ins or other spooling problems. It does lessen the amount you can get onto the spool, however.

Lots of conventional tackle bass guys love it. Should make fine fly line backing.

Good Luck!