As others have said, PWs are in the round wound family, and BFs are in the flats family. I really like the tone of each, but prefer the feel of the BFs. Yes, a little sticky, but smoother than the PWs, which have a sort of coarse texture to them.
...I wish I liked the feel of the PWs more, but I don't love it.
When I tried the PWs for the first time, I had been using flats almost exclusively for about a year. So, their "smooth texture" I had read about didn't exactly blow me away as they felt like any rounds under my fingers.
Then I went on a spree trying several sets of rounds for the next year, and when I came back to the PWs eventually, that's when I realized how smooth they really were in comparison. So, I guess it's all in one's perspective as to how "smooth" or "coarse" a set of strings can feel.