Bits of yarn cut up into various lengths and tied together to form great lengths of one yarn. Another yarn is carried for continuity. Using similar fibre content will assist in the felting process, otherwise you can get wicked colour and texture. For tensions, well, it doesn't count too much in this style. I'll try to get an image of my girlfriend scarves she knitt. Gorgeous! You can see her for miles. She is motivation in action.
When I started knitting, I was disappointed with the yarn available about town. My girlfriend and I would scour the local thrift shops to find casted yarn. We found some great scores and some nasties. Like old lady smelling Acrylon. Once I found 9 balls of alpacca, thank you whoever that was! Not long after that I found about 12 balls of this blush coloured boucle, an alpacca and polyester blend. It was wonderful. I knit up my first (S n' B) sweater with it. I was going to make a matching dog sweater, but the dog doesn't live here anymore. Even though the dog is gone, it doesn't help not having great yarns to motivate and activate.
My sister, Ms. Twiss of www.TwistersYarns.blogspot.com is the spinner of the family. Well, she lives 3000km away, so that is a far away thought... But it got me thinking. I could make my own yarn. I was trying to figure things out and came across Prudence Mapstone, she is a freeform knitter. I figured I could borrow some aspects of her work. You can read a review of her book "Free Form Knitting" here.