I believe it was acrylic. I like to join mine at the beginning of the row. I just pick up the new yarn and knit with it. On the following row, I'll give it a tug to snug it up. I leave the ends dangle until I'm ready to finish a piece off, then I weave in the ends. I might knot the two yarns together loosely, but I undo them when I'm ready to weave in the ends.